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Article

Accelerated Electrons Transfer and Synergistic Interplay of Co and Ge Atoms (111 Crystal Plane) Activated by Anchoring Nano Spinel Structure Co2GeO4 onto Carbon Cloth Composite Electrocatalyst for Highly Enhanced Hydrogen Evolution Reaction

by
Chen Chen
1,*,
Jiarui Zhu
1,
Ting Cheng
1,2,
Fei Wu
1,
Jun Xie
1,
Dawei He
1,
Youzhi Dai
3,
Xiao Zhang
4,
Le Zhao
1 and
Zhongsheng Wei
1
1
School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212100, China
2
School of Environmental Ecology, Jiangsu City Vocational College, Nanjing 210017, China
3
College of Environment and Resource, Xiangtan University, Xiangtan 411105, China
4
Nanjing University and Yancheng Academy of Environmental Protection Technology and Engineering, Yancheng 224000, China
*
Author to whom correspondence should be addressed.
Catalysts 2024, 14(10), 664; https://doi.org/10.3390/catal14100664
Submission received: 5 August 2024 / Revised: 21 September 2024 / Accepted: 23 September 2024 / Published: 25 September 2024
(This article belongs to the Special Issue Environmental Applications of Novel Nanocatalytic Materials)
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Abstract

:
The electrochemical hydrogen evolution reaction (HER) was considered to be a promising strategy for future clean energy. In this work, a composite electrocatalyst (designated as CGO36@CC) was synthesized through anchoring of nano spinel structure Co2GeO4 onto carbon cloth fibers and exhibited outstanding electrocatalytic performance for HERs in an alkaline medium. The characterization outcome established that, after 36 h of hydrothermal reaction, nano spinel structure Co2GeO4 particles (exposed abundant 111 crystal planes) were stably loaded onto a carbon cloth fiber surface, and this structural configuration facilitated the electrons transferring between each other. In addition, the electrochemical analysis revealed that the incorporation of nano spinel structure Co2GeO4 and carbon cloth significantly augmented the electrochemical activity value of the composite and efficiently enhanced the HER performance. Notably, the overpotential was merely 96 mV at 10 mA·cm−2 current density, and the Tafel slope was only 48.9 mV·dec−1. Moreover, CGO36@CC displayed remarkable catalytic activity and sustained HER catalytic stability. The theoretical catalytic prowess of CGO36@CC stemmed from the collaborative influence of germanium and cobalt atoms within the exposed 111 crystal plane of the Co2GeO4 molecular framework. The amalgamation of Co2GeO4 with carbon cloth fiber conferred upon the composite electrocatalyst both superior theoretical catalytic activity and enhanced electron transfer capability. This work provides a novel strategy for exploring a highly efficient composite electrocatalyst combined transition metal with carbon material to accelerate the HER activity.

1. Introduction

The continuous reliance on fossil energy in contemporary society has exacerbated environmental pollution [1,2], and urgency surrounds the quest for alternative renewable energy sources to supplant traditional fossil fuels [3]. Hydrogen energy as one of the alternatives stands out due to its high-energy-density and clean secondary energy source, rendering it a promising solution to address the energy crisis [4]. Photocatalysis and electrocatalytic hydrogen evolution were considered to be two promising pathways for obtaining clean hydrogen energy. The photocatalytic reaction utilizes a photocatalyst and light to degrade organic pollutants into carbon dioxide and water [5,6]. The free radicals generated are capable of reducing the H2O molecules adsorbed on the surface of the catalyst to H2; however, the hydrogen production performances of numerous photocatalysts need to be further improved [7]. Notably, the electrolysis of water for hydrogen production-yielding H2 and O2 as final products emerges as a straightforward and environmentally friendly technology and has attracted widespread attention from researchers [8]. In the electrochemical process, the catalyst electrode, serving as the central component, commands primary focus in current research [9]. Electrochemical water splitting, which consists of two half-reactions occurring at the anode and cathode, is fundamental to hydrogen production. The oxygen evolution reaction (OER) takes place at the anode, while the hydrogen evolution reaction (HER) occurs at the cathode [10]. Presently, the hydrogen evolution reaction is esteemed as one of the most effective methods for generating high-purity hydrogen at the cathode [11]. In the standard state, the voltage of overall water splitting requires a minimum potential of 1.23 V in theory. Whereas, to overcome the sluggish kinetics and electrolyte resistance in the field of overpotential, excess energy is demanded, and the operating voltage required is greatly higher than the theoretical potential [12,13]. Accordingly, the exploration of high-activity electrochemical catalysts is urgently required to accelerate the electrochemical reaction process, effectively mitigate the overpotential, and expedite the reaction kinetics of water splitting.
Presently, precious platinum metal and its composites, such as Pt/C and RuO2/IrO2, stand as the most efficacious HER and OER catalysts, owing to their rapid reaction kinetics and low overpotential in alkaline media [14,15]. Nevertheless, their advancement and application are impeded by their high cost and limited reserves in nature. In addition to platinum-based materials, transition metals (primarily Fe, Co, Ni, etc.) and their composite catalysts are deemed promising due to their affordability, abundance, and high theoretical activity for HER catalytic performance [16,17]. Consequently, they represent a viable alternative to precious platinum metal in catalytic electrode applications [18,19]. Notably, cobalt-based catalysts have recently garnered significant attention as electrocatalysts due to their favorable catalytic activity, low cost, and high stability [20]. Because of its special external electronic structure, many reports focus on enhancing HER performance through cobalt-based composite materials. For instance, Dai et al. prepared an electrocatalyst containing the active components of Co and CoO fixed on N-doped carbon material, and the electrocatalyst demonstrated enhanced charge transfer efficiency and notable electrocatalytic performance, exhibiting a low overpotential of 152 mV for the HER at a current density of 10 mA·cm−2 [21].
Shu et al. synthesized an electrocatalyst, Co/P-doped carbon material via the process of chemical vapor deposition and obtained a low overpotential of 240 mV for the HER at 10 mA·cm−2 [22]. Hence, cobalt was deemed to be crucial to construct superior electrocatalysts for the HER process. In most situations, to obtain higher efficiency electrocatalytic materials, a feasible approach is to combine active component of Co-based materials with other conductive substances.
In addition to cobalt, recently, germanium, which has been rarely studied for electrocatalysis, has been shown to have a promoting effect on electrocatalysis process. For example, Xiao et al. synthesized CuGeO3 micro-nanomaterial through the hydrothermal method, and its hydrogen evolution overpotential under acidic conditions was 135 mV (10 mA·cm−2), and the Tafel slope was 98 mV·dec−1 [23]. Then, Ng et al. prepared diverse variants of germananes and investigated their fundamental properties. They found that the functionalized germananes were proved to function as photoelectrocatalysts in the HER process, and the performance was affected by the functionalized germanane groups, where the lowest overpotential for an electrocatalytic HER was achieved via CH2CH2CH2OH termination [24]. Zhou et al. synthesized mesoporous Na4Ge9O20 microcrystals electrocatalyst anchored to 5 wt% Pt nanoparticles and obtained Pt/Na4Ge9O20 composite. The composite exhibited substantially improved electrocatalytic activity and excellent stability for the oxygen reduction reaction in both acidic and alkaline environments [25]. As far as we know, there are few reports about composite electrocatalysts including a cobalt and germanium component, and their electrocatalytic properties and performances still require illustration. Moreover, effective electrocatalytic materials require not only favorable theoretical catalytic functionality, but also outstanding electron transfer capabilities, which is imperative for effective electrocatalysts. The conventional strategy of loading active metallic or metallic oxide onto a conductive substrate surface (typically a glassy carbon electrode) is acknowledged for improving the electronic conductivity through facilitating the electron transfer between supports and catalysts. In particular, a wide range of carbon materials, including carbon cloth, carbon paper, and carbon nanotubes, are increasingly being used as excellent conductive substrates for electrocatalysts. In this regard, Chen et al. synthesized composite electrocatalysts, combined cobalt nanozeolite with carbon nanotubes with different rations (CoZ@xCNT), displayed highly efficient catalytic activities for OER, and the strong interaction between cobalt nanozeolite and carbon nanotubes greatly enhanced electron transfer, resulting in a low overpotential of 277 mV and a Tafel slope of 86.5 mV·dec−1 [26]. So far, new composite electrocatalysts with remarkable electrocatalytic activities still require development, and the electron transfer process, structural characteristics, and comprehensive electrocatalytic performances and mechanisms also remain to be revealed.
Drawing from the above analysis and prior research, herein, a new kind of cobalt- and germanium-based nano spinel structure material of Co2GeO4, synthesized successfully by combining cobalt chloride with germanium oxide, was utilized as an efficient electrocatalyst for the HER. Then, a highly efficient and stable electrochemical catalyst (CGO36@CC) was gained through further loading of the nano spinel structure Co2GeO4 on carbon cloth fibers as the conductive support. The obtained composites were examined via a series of modern instruments to characterize the fundamental properties, including morphological attributes, mineral phases, surface elemental compositions, and the corresponding valence states. Subsequently, electrochemical activities were evaluated through comprehensive electrochemical experiments. The electrocatalyst CGO36@CC was proved to significantly enhance the electrocatalytic performance of HERs, with a low overpotential of 96 mV at 10 mA·cm−2 and a Tafel slope of 48.9 mV·dec−1. The amalgamation of the nano spinel structure Co2GeO4 with carbon cloth conferred upon the composite electrocatalyst not only superior theoretical catalytic prowess but also enhanced electron transfer capability. The theoretical catalytic efficiency of the nano spinel-structured Co₂GeO₄ arises from the synergistic interaction between germanium and cobalt atoms within the molecular framework’s 111 crystal plane.

2. Results and Discussions

2.1. XRD

Figure 1a–c present the XRD analysis results of carbon cloth, CGOx, and CGOx@CC materials. As shown in Figure 1a, the primary XRD peaks of the carbon cloth were positioned at 2θ/° (crystal plane): 25.3° and 43.3°, which were the characteristic peaks of carbon cloth. Subsequently, as Figure 1b depicts, the main XRD peaks of CGOx samples were concentrated at 2θ/°: about 30.4°, 36.0°, 44.1°, 58.1°, and 63.7°. By comparison with the standard database, the crystal structure of CGOx was identified as PDF#10-0464 (Co2GeO4). Then, by comparison, it also could be found that these main peaks only appeared after 12 h of hydrothermal reaction and gradually increased with the extension of reaction time. Obviously, such results implied that the Co2GeO4 crystal only began to appear after 12 h of reaction, and the crystal structure gradually matured with the increasing reaction time. Moreover, the XRD analysis results of the CGOx@CC composites revealed the simultaneous presence of the main peaks corresponding to Co2GeO4 and carbon cloth, each displaying varying intensities. These findings suggested that all the CGOx@CC samples were composite materials comprising Co2GeO4 and carbon cloth. Furthermore, Figure 1d juxtaposes the XRD analysis results of the synthesized CGO36 composite with the calculated results of the standard spinel crystal model (insert picture). It was discernible that the position and relative intensity of the main peaks in the two curves exhibited substantial agreement. Hence, it could be inferred that the theoretical structure depicted in the illustration aligned with the actual crystal structure of Co2GeO4. This theoretical structure served as the basis for subsequent DFT calculations.

2.2. SEM

The SEM morphology analysis results for the original carbon cloth and CGOx@CC composites are presented in Figure 2. Obviously, it was revealed that the carbon cloth exhibited a micron-sized fiber structure (diameter of about 20–30 μm). Then, after the hydrothermal reaction, the reaction products began to appear on the surface of carbon cloth fibers (Figure 2b–d), indicating that they tend to form near the carbon cloth fibers. Subsequently, through the comparison of Figure 2b–d, it was revealed that as the reaction time increased, the morphology of products gradually changed. When the reaction lasted for 18 h, only slight irregular products appeared on the carbon cloth fibers. Subsequently, when the reaction lasted for 24 h, the products appearing on the carbon cloth fiber increased, while still maintaining an irregular morphology. Finally, when the reaction time reached 24 h, the reaction products loaded on the surface of carbon cloth fibers transformed from irregular morphology to regular crystals (Figure 2d,e). As we know, this regular pyramid belongs to a typical spinel structure, which is consistent with the theoretical crystal morphology shown in Figure 1d (insert picture). Then, this crystal structure exposed a large amount of its 111-crystal plane, which would provide a large number of active surfaces and sites for the electrocatalytic hydrogen evolution process. Next, Figure 2f illustrates the EDX mapping analysis results of the area of Figure 2e. As it shows, all the carbon, cobalt, germanium, and oxygen elements exhibited strong distribution within the areas. As we know, the carbon element was the primary constituent of the carbon cloth. The abundant appearance of cobalt, germanium, and oxygen elements indicated that the crystal reaction product was composed of these three elements, which was consistent with its crystal molecular formula (Co2GeO4). Furthermore, according to the morphology and XRD analysis results (Figure 1 and Figure 2), Figure 2g displays the summarized theoretical process of Co2GeO4 crystal formation. After 12 h of hydrothermal reaction, preliminary irregular cobalt germanium crystals began to appear on the surface of carbon cloth fibers. As the reaction time prolonged (more than 18 h), the quantity of reaction products gradually increased, but still maintained irregular morphology. After further hydrothermal reaction (more than 24 h), the molecular structure of the reaction product gradually became regular and formed a spinel crystal appearance.

2.3. XPS

X-ray photoelectron spectroscopy (XPS) was employed to conduct further analysis of the surface elemental composition of CGOx@CC, with the results presented in Figure 3 and Figure S1. Wide scanning results depicted in Figure 3a revealed XPS peaks for CGOx@CC composite at energies of about 30.3, 61.2, 101.8, 122.2, 182.1, 283.5, 341.1, 527.2, 715.6, 780.2, 800.4, 925.1, 978.5, 1217.3, and 1250.2 eV. These peaks predominantly corresponded to Ge3d, Co3p3/2, Co3p1/2, Ge3p, Ge3s, C1s, Ge LMM, O1s, Co LMM, Co2p3/2, Co2p1/2, O KLL, Ge2p3/2, and Ge2p1/2, indicating the presence of cobalt, germanium, and oxygen elements in the CGOx@CC composites. Next, an in-depth comparison between the results of all CGOx@CC composites revealed that the peaks related to germanium (Ge3d, Ge3p, Ge3s, Ge LMM, Ge2p3/2, and Ge2p1/2) and cobalt (Co3p3/2, Co3p1/2, Co2p3/2, and Co2p1/2) elements could only be clearly observed after 12 h of reaction and then gradually increased with the prolongation in reaction time. Obviously, the results suggested that, consistent with the above analysis of SEM and XRD, the Co2GeO4 only began to form on the surface of carbon cloth fibers after 12 h of reaction and gradually increased with the extension in reaction time.
Additionally, high-resolution XPS spectrum analysis results displayed in Figure 3b and Figure S1a revealed primary Co 2p peaks for the CGOx@CC composites (except CGO6@CC) at binding energies of 780 and 795 eV, likely corresponding to Co2p3/2 and Co2p1/2, as determined by the peak areas’ positions and size ratios. Furthermore, two distinct satellite peaks (at about 785 eV and 806 eV) were observed adjacent to the two main peaks. This observation suggested that the cobalt element in all the CGOx@CC composites (except CGO6@CC) existed predominantly in the +2 oxidation state [20]. Moreover, all the CGOx@CC materials (except CGO6@CC) exhibited a Ge3d characteristic peak at about 32 eV (Figure 3c and Figure S1b). According to reference [27], the appearance of the Ge3d peak indicated that germanium in all the samples predominantly existed in the +4 oxidation state. Additionally, the O1s peak of all the CGOx@CC samples (except CGO6@CC) exhibited two discernible peaks at about 530 and 532 eV (Figure 3d and Figure S1c), which might correspond to two different oxygen conditions. Among them, the larger peaks should be attributed to oxygen in the lattice of the molecular structure of Co2GeO4, and the other smaller peak may be due to adsorbed oxygen on the material surface [28,29]. While for the CGO6@CC material, only one peak appeared at 530 eV, which once again indicated that no Co2GeO4 was formed on the surface of carbon cloth fiber at this time. Furthermore, through careful comparison, it could be observed that as the reaction time increased, the peak positions of Co2p- and Ge3d-related peaks shift slightly towards the increasing direction. At the same time, the position of the O1s peak shifts slightly towards a decreasing direction. According to basic XPS technology knowledge, the shift of element peaks towards higher energy is usually related to the loss of electrons, while if they shift towards lower energy, it often indicates that the element has gained electrons. Hence, the XPS peak shifts in different directions exhibited by cobalt, germanium, and oxygen elements should suggest the continuous electron transfer between them as the reaction progresses. This mutual electron movement should lead to a gradual change in the chemical bonds between cobalt/germanium and oxygen atoms during the hydrothermal reaction process, which might be a manifestation of gradual maturation and regularity of the spinel Co2GeO4 crystal.

2.4. Electrochemical Catalytic Performance

As is well known, the electrochemical active surface area (ECSA) of a catalyst is directly linked to its electrocatalysis performance. Figure 4 and Figure S2 presented the results of electrochemically active surface area tests conducted on carbon cloth and CGOx@CC composites, showcasing cyclic voltammetry (CV) curves for non-Faraday regions. Upon examination of Figure 4 and Figure S2, it became apparent that the charging/discharging currents of CGOx@CC composites were significantly higher than that of the pure carbon cloth at the same scanning speed. These findings suggested that the loading of Co2GeO4 onto the carbon cloth surface could effectively enhance its electroactive activity. Then, among all the composite materials, both CGO36@CC and CGO48@CC composites exhibited the highest and similar charge/discharge current values, indicating that the spinel Co2GeO4 with a regular crystal structure obtained higher electroactive activity. Furthermore, Figure 4e and Figure S2d present the results of linear analysis, illustrating the relationship between scanning speed and charge/discharge current. The slope of the line represents the capacitance (Cdl), which was considered to be positively correlated with the ECSA value. As depicted, the Cdl values for all materials were 0.131 (carbon cloth), 2.21 (CGO6@CC), 3.03 (CGO12@CC), 4.28 (CGO18@CC), 5.12 (CGO24@CC), 6.14 (CGO36@CC), and 6.13 mF·cm−2 (CGO48@CC), respectively. It was evident that the incorporation of Co2GeO4 significantly augmented the electrochemical activity of the composite material. The regular spinel crystal structure (CGO36@CC and CGO48@CC) contributed to further improvement in electrochemical activity.
The assessment of electrochemical hydrogen evolution performance usually involves conducting linear scanning voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) tests. Figure 5 and Figure S3 present the LSV and EIS test results conducted on CC and CGOx@CC composites. From the observations, it was clear that at a current density of 10 mA·cm−2, the overpotentials for the various samples were measured as follows: 252 mV for carbon cloth, 263 mV for CGO6@CC, 204 mV for CGO12@CC, 140 mV for CGO18@CC, 105 mV for CGO24@CC, 96 mV for CGO36@CC, and 98 mV for CGO48@CC. Likewise, at current densities of 100 and 500 mA·cm−2, the order of HER overpotentials remained consistent (carbon cloth > CGO6@CC > CGO12@CC > CGO18@CC > CGO24@CC > CGO36@CC ≈ CGO48@CC). Further analysis was conducted based on the LSV data presented in Figure 5a and Figure S3a, revealing the Tafel slopes of all the materials as 158 (carbon cloth), 184.8 (CGO6@CC), 114.3 (CGO12@CC), 72.3 (CGO18@CC), 52.1 (CGO24@CC), 48.9 (CGO36@CC), and 49.1 (CGO48@CC) mV, respectively (Figure 5c and Figure S3c). The Tafel slope value of all materials suggested adherence to the Volmer–Heyrovsky reaction mechanism, with the Volmer reaction serving as the controlling step. Notably, the CGO36@CC and CGO48@CC composites exhibited the similar lowest Tafel slope, suggesting that in the HER process, as the current increased by ten times, the two catalytic systems required the lowest potential value increase. Additionally, Table 1 provided a summary of the electrochemical HER performance of recent cobalt-related materials. It was evident from the table that the catalytic efficiency of the CGO36@CC composite in this study exhibited obvious advantages compared with other materials (including Co2GeO4 loaded on Ni Foam material), indicating technical feasibility in the HER process. Moreover, Figure 5d and Figure S3d illustrate the electrochemical impedance analysis results of the HER for all the reaction systems. Through electrochemical analog circuits analysis, all the internal resistances (RΩ) were determined to be about 2.7 Ω. Subsequently, the charge transfer resistance (Rct) for all the reaction systems was found to be 27.3 (carbon cloth), 20.2 (CGO6@CC), 17.7 (CGO12@CC), 12.4 (CGO18@CC), 7.66 (CGO24@CC), 6.06 (CGO36@CC), and 5.96 (CGO48@CC) Ω, respectively. Notably, the CGO36@CC and CGO48@CC composites exhibited the similar lowest charge-transfer resistance value, which aligned with their superior electrochemical HER performance. Overall, based on all the electrochemical test results above, it could be clearly seen that loading Co2GeO4 on carbon cloth fibers could obtain composite materials with significant electrocatalytic activity. Among all composite materials, CGO36@CC and CGO48@CC displayed similar catalytic abilities, which were significantly higher than other materials. Combining the material characterization results above, their catalytic abilities should benefit from a regular spinel crystal Co2GeO4 structure on carbon cloth fibers. From the perspective of synthesis cost, the CGO36@CC composite with shorter reaction time is more economical and has greater potential for application in nature. Therefore, CGO36@CC is considered to be the optimal composite material, and the research on catalytic stability is subsequently conducted.
In addition to excellent catalytic performance, catalytic stability was also a crucial capability for electrochemical materials. Figure 6 presents the results of the electrochemical stability test conducted on the CGO36@CC composite. Upon examining the fluctuation in the analysis results depicted in Figure 6a, it was evident that the current density could remain stable for 25 h at different hydrogen evolution potentials (100, 196, 246, and 281 mV). Furthermore, the results displayed in Figure 6b indicate that after 5000 CV cycles, the HER overpotential of the CGO36@CC composite only increased to 150 mV (at 10 mA·cm−2), 301 mV (at 100 mA·cm−2), and 519 mV (at 500 mA·cm−2). Thus, it was apparent from the findings in Figure 6a,b that the CGC36@CC catalytic system exhibited favorable electrochemical stability. Moreover, the stability of both the material structure and its elemental composition was also essential for catalytic materials. Figure 6c compared the XRD patterns of the original CGO36@CC composite with those after the stability testing. As observed from Figure 6c, after the stability test, the primary XRD peaks of both carbon cloth and Co2GeO4 were still clearly visible. This suggested that the crystal phase structure of the synthesized composite remained stable both prior to and following the hydrogen evolution reaction. Subsequently, Figure 6d–f and Figure S4 provided a comparison of the XPS analysis results obtained from CGO36@CC before and after the stability testing. As depicted in Figure S4, the main XPS peak positions and sizes displayed no significant differences, suggesting that the elemental composition of the CGO36@CC composite remained essentially stable before and after stability testing. Furthermore, the high-resolution XPS results of Co 2p (Figure 6d) revealed that the XPS peak shape of the two main divided peaks (Co2p1/2 and Co2p3/2) with their satellite peaks remained consistent. These results indicated minimal variation in the existence form of the Co element. Similarly, for the germanium and oxygen elements (Figure 6e,f), their XPS peaks also remained basically stable and only very slight shifts could be found in the peak shape, division, and position. Based on the analysis results from both XRD and XPS, it could be inferred that the composite of CGO36@CC maintained excellent stability in its mineral phase structure and elemental composition before and after the stability testing. Coupled with its acceptable electrocatalytic stability, it is concluded that the CGO36@CC composite exhibited excellent catalytic stability.
As is well understood, the efficient transport of electrons to catalytic sites is paramount for achieving excellent electrocatalytic performance. In this context, the suitable conductive substrate played a critical role in enhancing the HER performance of electrocatalysts. In our study, the material characterization results clearly presented that, after 36 h of reaction, a large amount of nano spinel Co2GeO4 formed on the surface of the carbon cloth fiber. Based on this composite structure, we believe that carbon cloth fibers, being typical carbon materials, could rapidly transfer electrons to the catalytic active sites of Co2GeO4 on their surface. Moreover, outstanding catalytic ability is also vital for electrocatalysts. The findings also revealed that there was an abundant appearance of Ge and Co atoms in the crystal surface, forming favorable electrocatalytic hydrogen evolution, which might be attributed to the synergistic effect of Ge and Co in the electrocatalytic process. We performed possible reaction pathway calculations using Density Functional Theory (DFT), as detailed in the Supplementary Materials of “HER reaction mechanism”.

3. Experiment and Methods

3.1. The Synthesis Process of Catalytic Materials

The reagents employed in this experimental investigation, including cobalt chloride hexahydrate, germanium oxide, sodium hydroxide, and potassium hydroxide, were obtained from Sigma Reagents Company and conformed to analytical purity standards. The carbon cloth utilized in this study was sourced from Suzhou Sinero Technology Co., Ltd. (Suzhou, China), possessing the following initial property specifications: a thickness of 0.35 mm, nominal basis weight of 140 g/m2, Gurley air permeability of 1.56, and plane resistance of 1.50 mΩ/cm2. Initially, the carbon cloth underwent heat treatment at 450 °C for two hours, followed by gradual cooling to room temperature to enhance its hydrophilicity as a conductive substrate material [40]. The synthesis process of pure Co2GeO4 referred to the work of other researchers [27], and then, based on the actual preliminary data of this study, modifications and optimizations have been made in the synthesis reagent ratio, reaction time, and so on. The synthesis procedure entailed the following steps: initially, 0.0002 mol of CoCl2·6H2O was dissolved in 60 mL of distilled water. Separately, 0.0002 mol of GeO2 and 0.0018 mol of NaOH were dispersed in another 60 mL of distilled water, followed by stirring for 45 min at room temperature. Subsequently, the two solutions were combined and stirred continuously for 1 h at room temperature until the mixture assumed a lavender hue. The mixture was then placed into a 100 mL Teflon-lined stainless-steel autoclave for a hydrothermal reaction, which was carried out at 160 °C for 6 to 48 h. After cooling, the reaction products were subjected to several centrifugal washes with deionized water and ethanol, followed by drying in a blast oven at 90 °C for approximately 12 h until achieving a constant weight. After multiple weighing, each reaction unit can obtain 0.021–0.022 g of reaction product. Assuming that all reaction products strictly follow the molecular formula of Co2GeO4, the actual reaction yield per unit reaction process is about 82.3% to 86.3%. The obtained samples were named CGOx, where x represented the hydrothermal reaction time (6, 12, 18, 24, 36, and 48). The preparation protocol for the composite material remained consistent with the previously described method for pure Co2GeO4, with the exception of incorporating a 1 × 1 cm carbon cloth into the mixture before the hydrothermal reaction. The synthesis process of CGOx and CGOx@CC materials is depicted in Figure 7. The synthesized composite material (CGOx@CC) was subsequently affixed to an electrode clamp and directly utilized as the working electrode.

3.2. Materials Characterization

To comprehensively assess the synthesized composite materials, diverse properties of the electrocatalysts were characterized utilizing a range of sophisticated analytical techniques. Principally, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDX) were utilized. The characterization details were provided below: morphological features and microelement composition of the materials were examined utilizing a HITACHI scanning electron microscope (Regulus 8100, Hitachi, Tokyo, Japan). This instrument facilitated detailed observation and analysis of the material’s surface structure and elemental distribution; XRD patterns of powder samples were obtained utilizing a XD-6 polycrystalline X-ray diffractometer (Beijing Puxi, Beijing, China); Cu-Kα radiation (λ = 1.54056) was employed to analyze the mineral phase composition of the synthesized materials. This technique allowed for the identification and analysis of crystalline phases present in the samples; examination of the surface chemistry and elemental composition of the materials was performed using a PHI 5000 VersaProbe XPS equipment (Physical Electronics, Chanhassen, MN, USA). XPS analysis provided insights into the chemical states and bonding environments of the elements within the samples. Through the use of these advanced characterization techniques, a thorough understanding of the structural, morphological, and chemical properties of the synthesized composite materials was achieved, facilitating insights into their electrocatalytic performance and potential applications.

3.3. Electrochemical Experiment

The electrochemical hydrogen evolution reaction (HER) experiments were performed using a standard three-electrode system. The experimental setup included the CHI 660E electrochemical workstation (Shanghai Chenhua, Shanghai, China) as the electrochemical detection instrument. A total of 1 mol/L KOH solution was used as the electrolyte, with a Graphite rod electrode serving as the counter electrode and a mercury/mercury oxide electrode functioning as the reference electrode. For CGOx@CC materials, the synthesized flaky catalyst sample was directly utilized as the working electrode, with the working area set at 0.25 cm2. The conversion formula relating the test potential to the standard reversible hydrogen electrode (RHE) potential was given with Equation (1).
ERHE = EHg/HgO + 0.098 + 0.0591pH
Before testing, the electrolyte was purged with high-purity N2 for 20 min to remove dissolved oxygen. Linear scanning voltammetry with compensation (IR-corrected LSV) testing was conducted over a potential range of −1.92 V to −0.92 V (vs. Hg/HgO). The scanning speed was set at 2 mV/s, with a scanning accuracy of 0.0001. The Tafel slope was determined by analyzing the stable regions of the LSV curve. Electrochemical impedance spectroscopy for the HER was performed at a potential of −1.12 V (vs. Hg/HgO). The scanning frequency ranged from 1 to 10,000 Hz, with an amplitude of 5 mV. The impedance spectrum data were then fitted using suitable analog circuits with the help of relevant software(Zview 2.70). Additionally, the electrochemical active area was assessed using cyclic voltammetry (CV) curves, accounting for non-Faradic contributions. The potential range extended from −0.1 V to −0.2 V (vs. Hg/HgO), with the scanning rate varying from 10 mV/s to 120 mV/s. In the electrochemical stability assessment, the hydrogen evolution reaction (HER) time–current (i-t) curve was monitored for 100 h, with overpotentials of 100, 196, 246, and 281 mV, each maintained for 25 h. Subsequently, the IR-corrected LSV curve of the material was re-evaluated after 5000 cyclic voltammetry (CV) cycles.
To illustrate the electrocatalytic mechanism in the hydrogen evolution reaction process, the theoretical calculations were carried out using the Vienna Ab initio Simulation Package (VASP) VASP version 6.4.2 in combination with spin-polarized Density Functional Theory (DFT), as detailed in the Supplementary Materials of “DFT Theoretical calculation”.

4. Conclusions

In summary, a composite material of CGO36@CC was synthesized via the hydrothermal loading of nano spinel Co2GeO4 crystal onto carbon cloth fibers. It could be utilized as a superior electrocatalyst to improve the electrochemical activities of the HER in 1M KOH solution. As expected, the combination of spinel Co2GeO4 crystal and carbon cloth fiber could effectively enhance the electrochemical activity of the HER. The CGO36@CC composite displayed a low overpotential of 96 mV to drive the HER at 10 mA·cm−2 and a small Tafel slope of 48.9 mV·dec−1. Moreover, the composite electrocatalyst demonstrated long-term electrocatalytic stability for up to 100 h (under different HER potentials), and little overpotential escalation even after 5000 CV cycles. Moreover, the synergistic interplay between germanium and cobalt atoms within the (111) crystal plane of the Co2GeO4 molecule propelled the effective advancement of the entire HER catalytic reaction. This finding provides a promising strategy for the exploration of highly efficient electrocatalysts for hydrogen evolution reactions.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal14100664/s1, Figure S1: The high-resolution XPS results of Co 2p(a), Ge 3d (b) and O 1s (c) of CGO6@CC, CGO12@CC and CGO48@CC materials; Figure S2: The CV curves of non-Faraday region (different scanning speeds) (a: CGO6@CC, c: CGO12@CC and CGO48@CC); plots of capacitive current density vs different scan rate for Cdl (d); Figure S3: The HER IR-corrected LSV polarization curves a and b(detail), Tafel plots (c), EIS spectra (d) of Carbon cloth, CGO6@CC, CGO12@CC and CGO48@CC materials; Figure S4: The XPS full spectrum scanning of CGO36@CC composite before and after the stability testing; Figure S5: The optimized configurations for catalytic structures (Co active site), encompassing H2O molecule adsorption (a: *–H2O), co-adsorption of hydrogen atom and hydroxyl group (b: *–(H+OH)) and hydrogen atom adsorption (c: *–H) on the CGO (111) crystal plane; Figure S6: The optimized configurations for catalytic structures (Ge active site), encompassing H2O molecule adsorption (a: *–H2O), co-adsorption of hydrogen atom and hydroxyl group (b: *–(H+OH)) and hydrogen atom adsorption (c: *–H) on the CGO (111) crystal plane; Figure S7: The theoretical change of Gibbs free energy along HER catalytic path of CGO configuration; Figure S8: The theory cell (a) and surface structure (b: 111) of spinel Co2GeO4. References [41,42,43,44,45,46,47,48,49] are cited in the Supplementary Materials.

Author Contributions

Conceptualization, C.C., T.C. and Y.D.; methodology, J.Z. and C.C.; software, C.C. and J.Z.; validation, J.Z., F.W. and T.C.; formal analysis, J.Z. and F.W.; resources, C.C. and X.Z.; data curation, J.Z., J.X., D.H., L.Z. and Z.W.; writing—original draft preparation, J.Z. and F.W.; writing—review and editing, C.C. and T.C.; visualization, J.Z., F.W. and T.C.; supervision, C.C., Y.D. and X.Z.; project administration, C.C.; funding acquisition, C.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Zhenjiang City 2021 key research and development project (Social Development), grant number SH2021020.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Wang, L.; Song, A.; Lu, Y.; Duanmu, M.; Ma, Z.; Qin, X.; Shao, G. Strong and Hierarchical Ni(OH)2/Ni/rGO composites as multifunctional catalysts for excellent water splitting. Catalysts 2024, 14, 309. [Google Scholar] [CrossRef]
  2. Biehler, E.; Quach, Q.; Abdel-fattah, T.M. Application of platinum nanoparticles decorating mesoporous carbon derived from sustainable source for hydrogen evolution reaction. Catalysts 2024, 14, 423. [Google Scholar] [CrossRef]
  3. Jawale, D.V.; Fossard, F.; Miserque, F.; Geertsen, V.; Teillout, A.L.; De, O.P.; Mbomekallé, I.M.; Gravel, E.; Doris, E. Carbon nanotube-polyoxometalate nanohybrids as efficient electro-catalysts for the hydrogen evolution reaction. Carbon 2022, 188, 523–532. [Google Scholar] [CrossRef]
  4. Zhang, C.; Liu, Y.; Wang, J.M.; Li, W.P.; Wang, Y.L.; Qin, G.H.; Lv, Z.G. A well-designed fencelike Co3O4@MoO3 derived from Co foam for enhanced electrocatalytic HER. Appl. Surf. Sci. 2022, 595, 153532. [Google Scholar] [CrossRef]
  5. Chen, C.; Wang, L.; Cheng, T.; Zhang, X.-Q.; Zhou, Z.-Y.; Zhang, X.; Qi, X. Ag3PO4/AgSbO3 composite as novel photocatalyst with significantly enhanced activity through a Z-scheme degradation mechanism. J. Iran. Chem. Soc. 2022, 19, 821–838. [Google Scholar] [CrossRef]
  6. Cheng, T.; Chen, C.; Wang, L.; Zhang, X.; Ye, C.-H.; Deng, Q.; Chen, G. Synthesis of fly ash magnetic glass microsphere@BiVO4 and its hybrid action of visible-light photocatalysis and adsorption process. Pol. J. Environ. Stud. 2021, 30, 1–14. [Google Scholar] [CrossRef]
  7. Chen, C.; Wang, L.; Cheng, T.; Zhang, X.; Tian, Y.; Shi, Y.-S. Sliver doped sodium antimonate with greatly reduced the band gap for efficiently enhanced photocatalytic activities under visible light (experiment and DFT calculation). Mat. Res. 2021, 24, e20210100. [Google Scholar] [CrossRef]
  8. Feng, C.Q.; Xin, B.W.; Li, H.L.; Jia, Z.; Zhang, X.L.; Geng, B.J. Agaric-like cobalt diselenide supported by carbon nanofiber as an efficient catalyst for hydrogen evolution reaction. J. Colloid Interface Sci. 2022, 610, 854–862. [Google Scholar] [CrossRef]
  9. Sun, K.Y.; Qiao, F.; Yang, J.; Li, H.T.; Cui, Y.; Liu, P.F. Fluff spherical Co-Ni3S2/NF for enhanced hydrogen evolution. Int. J. Hydrogen Energ. 2022, 47, 27986–27995. [Google Scholar] [CrossRef]
  10. Van der Zalm, J.M.; Quintal, J.; Hira, S.A.; Chen, S.; Chen, A.C. Recent trends in electrochemical catalyst design for hydrogen evolution, oxygen evolution, and overall water splitting. Electrochimi. Acta 2023, 439, 141715. [Google Scholar] [CrossRef]
  11. Tahir, M.; Pan, L.; Idrees, F.; Zhang, X.; Wang, L.; Zou, J.-J.; Wang, Z.L. Electrocatalytic oxygen evolution reaction for energy conversion and storage: A comprehensive review. Nano Energy 2017, 37, 136–157. [Google Scholar] [CrossRef]
  12. Ledezma-Yanez, I.; Wallace, W.D.Z.; Sebastian-Pascual, P.; Climent, V.; Feliu, J.M.; Koper, M.T.M. Interfacial water reorganization as a pH-dependent descriptor of the hydrogen evolution rate on platinum electrodes. Nat. Energy 2017, 2, 17031. [Google Scholar] [CrossRef]
  13. Xu, S.R.; Zhao, H.T.; Li, T.S.; Liang, J.; Lu, S.Y.; Chen, G.; Gao, S.Y.; Asiri, A.M.; Wu, Q.; Sun, X.P. Iron-based phosphides as electrocatalysts for the hydrogen evolution reaction: Recent advances and future prospects. J. Mater. Chem. A 2020, 8, 19729–19745. [Google Scholar] [CrossRef]
  14. Wu, Z.F.; Dang, D.; Tian, X.L. Designing robust support for Pt alloy nanoframes with durable oxygen reduction reaction activity. ACS Appl. Mater. Interfaces 2019, 11, 9117–9124. [Google Scholar] [CrossRef] [PubMed]
  15. Li, C.Q.; Baek, J.B. Recent advances in noble metal (Pt, Ru, and Ir)-based electrocatalysts for efficient hydrogen evolution reaction. Acs Omega 2020, 5, 31–40. [Google Scholar] [CrossRef] [PubMed]
  16. Wu, L.W.; Yao, Y.F.; Xu, S.Y.; Cao, X.Y.; Ren, Y.W.; Si, L.P.; Liu, H.Y. Electrocatalytic hydrogen evolution of transition metal (Fe, Co and Cu)–corrole complexes bearing an imidazole group. Catalysts 2023, 14, 5. [Google Scholar] [CrossRef]
  17. Zeng, J.; Cao, X.Y.; Xu, S.Y.; Qiu, Y.F.; Chen, J.Y.; Si, L.P.; Liu, H.Y. Electrocatalytic hydrogen evolution reaction of cobalt triaryl corrole bearing nitro group. Catalysts 2024, 14, 454. [Google Scholar] [CrossRef]
  18. Wu, L.Q.; Shi, D.D.; Yan, S.M.; Qiao, W.; Zhong, W.; Du, Y.W. Iron-doped cobalt nitride nanoparticles (Fe-Co3N): An efficient electrocatalyst for water oxidation. Int. J. Hydrogen Energy 2021, 46, 2086–2094. [Google Scholar] [CrossRef]
  19. Yu, F.; Yu, L.; Mishra, I.K.; Yu, Y.; Ren, Z.F.; Zhou, H.Q. Recent developments in earth-abundant and non-noble electrocatalysts for water electrolysis. Mater. Today Phys. 2018, 7, 121–138. [Google Scholar] [CrossRef]
  20. Zhang, H.-M.; Zhu, C. Co nanoparticles-embedded N, S-codoped hierarchically porous graphene sheets as efficient bifunctional electrocatalysts for oxygen reduction reaction and hydrogen evolution reaction. J. Mater. Res. Technol. 2020, 9, 16270–16279. [Google Scholar] [CrossRef]
  21. Dai, K.Q.; Zhang, N.; Zhang, L.L.; Yin, L.X.; Zhao, Y.F.; Zhang, B. Self-supported Co/CoO anchored on N-doped carbon composite as bifunctional electrocatalyst for efficient overall water splitting. Chem. Eng. J. 2021, 414, 128804. [Google Scholar] [CrossRef]
  22. Shu, Y.; Sasaki, K.; Fujimoto, Y.; Miyake, K.; Uchida, Y.; Tanaka, S.; Nishiyama, N. Electrochemical hydrogen evolution reaction over Co/P doped carbon derived from triethyl phosphite-deposited 2D nanosheets of Co/Al layered double hydroxides. Int. J. Hydrogen Energy 2022, 47, 10638–10645. [Google Scholar] [CrossRef]
  23. Xiao, Y.M.; Li, B.; Qin, L.Z.; Lin, H.; Li, Q.; Nie, M.; Li, Y.; Liao, B. CuGeO3 micro-nanomaterial as electrocatalyst for hydrogen evolution reaction. Catal. Commum. 2020, 144, 106075. [Google Scholar] [CrossRef]
  24. Ng, S.; Sturala, J.; Vyskocil, J.; Lazar, P.; Martincova, J.; Plutnar, J.; Pumera, M. Two-dimensional functionalized germananes as photoelectrocatalysts. Acs Nano 2021, 15, 11681–11693. [Google Scholar] [CrossRef] [PubMed]
  25. Zhou, X.; Chen, L.; Wan, G.; Chen, Y.; Kong, Q.; Chen, H.; Shi, J. Low Pt-loaded mesoporous sodium germanate as a high-performance electrocatalyst for the oxygen reduction reaction. ChemSusChem 2016, 9, 2337–2342. [Google Scholar] [CrossRef] [PubMed]
  26. Chen, C.; Hou, B.X.; Cheng, T.; Xin, X.; Zhang, X.; Tian, Y.; Wen, M.Y. The integration of both advantages of cobalt-incorporated cancrinite-structure nanozeolite and carbon nanotubes for achieving excellent electrochemical oxygen evolution efficiency. Catal. Commum. 2023, 180, 106708. [Google Scholar] [CrossRef]
  27. Choi, H.; Surendran, S.; Kim, D.; Lim, Y.; Lim, J.; Park, J.; Kim, J.K.; Han, M.-K.; Sim, U. Boosting eco-friendly hydrogen generation by urea-assisted water electrolysis using spinel M2GeO4(M = Fe, Co) as an active electrocatalyst. Environ. Sci-Nano 2021, 8, 3110–3121. [Google Scholar] [CrossRef]
  28. Dang, Y.-J.; Li, X.; Chen, Z.-K.; Ma, B.; Zhao, X.D.; Chen, Y.-T. Hierarchical CoO@MoN heterostructure nanowire array as a highly efficient electrocatalyst for hydrogen evolution. Chem. Eng. J. 2023, 477, 147154. [Google Scholar] [CrossRef]
  29. Pang, M.-J.; Long, G.-H.; Jiang, S.; Ji, Y.; Han, W.; Wang, B.; Liu, X.-L.; Xi, Y.-L.; Wang, D.-X.; Xu, F.-Z. Ethanol-assisted solvothermal synthesis of porous nanostructured cobalt oxides (CoO/Co3O4) for high-performance supercapacitors. Chem. Eng. J. 2015, 280, 377–384. [Google Scholar] [CrossRef]
  30. Wang, M.M.; Li, M.; Zhao, Y.L.; Shi, N.Y.; Zhang, H.; Zhao, Y.X.; Zhang, Y.R.; Zhang, H.R.; Wang, W.H.; Sun, K.A.; et al. Construction of N-doped carbon frames anchored with Co single atoms and Co nanoparticles as robust electrocatalyst for hydrogen evolution in the entire pH range. J. Energy Chem. 2022, 67, 147–156. [Google Scholar] [CrossRef]
  31. Cheng, H.; Liu, Q.; Diao, Y.W.; Wei, L.L.; Chen, J.H.; Wang, F.X. CoMo2S4 with superior conductivity for electrocatalytic hydrogen evolution: Elucidating the key role of Co. Adv. Funct. Mater. 2021, 31, 2103732. [Google Scholar] [CrossRef]
  32. Tian, Y.K.; Wen, M.; Huang, A.J.; Wu, Q.S.; Wang, Z.G.; Zhu, Q.J.; Zhou, T.; Fu, Y.Q. Significantly stabilizing hydrogen evolution reaction induced by Nb-doping Pt/Co(OH)2 nanosheets. Small 2023, 19, 2207569. [Google Scholar] [CrossRef] [PubMed]
  33. Yuan, S.S.; Xia, M.S.; Liu, Z.P.; Wang, K.W.; Xiang, L.J.; Huang, G.Q.; Zhang, J.Y.; Li, N. Dual synergistic effects between Co and Mo2C in Co/Mo2C heterostructure for electrocatalytic overall water splitting. Chem. Eng. J. 2022, 430, 132697. [Google Scholar] [CrossRef]
  34. Wang, P.Y.; Zhu, J.W.; Pu, Z.H.; Qin, R.; Zhang, C.T.; Chen, D.; Liu, Q.; Wu, D.L.; Li, W.Q.; Liu, S.L.; et al. Interfacial engineering of Co nanoparticles/Co2C nanowires boosts overall water splitting kinetics. Appl. Catal. B Environ. 2021, 296, 120334. [Google Scholar] [CrossRef]
  35. Gao, G.L.; Wei, D.W.; Li, L.; Wei, M.Q.; Chen, X.L.; Yu, Y.Y.; Yang, G.; Zhu, G.; Han, L.; Jia, J. Accordion-like Co-MOF derived heterostructured Co/CoP@PNC as highly efficient electrocatalyst for alkaline hydrogen evolution reaction. Int. J. Hydrogen Energy 2024, 51, 1333–1342. [Google Scholar] [CrossRef]
  36. Gong, C.; Zhao, L.; Li, D.M.; He, X.; Chen, H.; Du, X.; Wang, D.H.; Fang, W.; Zeng, X.H.; Li, W.X. In-situ interfacial engineering of Co(OH)2/Fe7Se8 nanosheets to boost electrocatalytic water splitting. Chem. Eng. J. 2023, 466, 143124. [Google Scholar] [CrossRef]
  37. Hu, X.; Zhou, J.; Bao, J.; Zhang, Y.; Qiao, J. Morphology and stoichiometry dependent electrocatalytic activity of Cu2ZnSnS4 for hydrogen evolution reaction (HER) with addition of nonionic surfactants. Electrocatalysis 2023, 15, 1–9. [Google Scholar] [CrossRef]
  38. Singh, T.I.; Rajeshkhanna, G.; Pan, U.N.; Kshetri, T.; Lin, H.; Kim, N.H.; Lee, J.H. Alkaline water splitting enhancement by MOF-derived Fe-Co-oxide/Co@NC-mNS heterostructure: Boosting OER and HER through defect engineering and in situ oxidation. Small 2021, 17, 2101312. [Google Scholar] [CrossRef]
  39. Gong, C.; Li, W.X.; Lei, Y.N.; He, X.; Chen, H.; Du, X.; Fang, W.; Wang, D.H.; Zhao, L. Interfacial engineering of ZIF-67 derived CoSe/Co(OH)2 catalysts for efficient overall water splitting. Compos. Part B-Eng. 2022, 236, 109823. [Google Scholar] [CrossRef]
  40. Liu, X.-Q.; Xu, W.; Zheng, D.-Z.; Li, Z.-F.; Zenga, Y.-X.; Lu, X.-H. Carbon cloth as an advanced electrode material for supercapacitors: Progress and challenges. J. Mater. Chem. A 2020, 8, 17938. [Google Scholar] [CrossRef]
  41. Yang, Y.; Zhao, X.; Liu, T.-Y.; Zhang, Y.-F.; Hu, Y.-J.; Liu, X.-F.; Wang, G.; Wang, D.-G.; Bi, J.-S.; Luo, Z.-J.; et al. The rational co-doping strategy of transition metal and non-metal atoms on g-CN for highly efficient hydrogen evolution by DFT and machine learning. Int. J. Hydrogen Energy 2024, 56, 949–958. [Google Scholar] [CrossRef]
  42. Hassan, R.; Ma, F.; Li, Y.; Hassan, R.; Qadir, M.F. Computational investigation of hydrogen evolution reaction on transition metal-doped monolayer VSe2: A DFT approach. J. Phys. Chem. Soids 2024, 192, 112070. [Google Scholar] [CrossRef]
  43. Cheng, T.; Wen, M.; Chen, C.; Zhu, J.; Dai, Y.; Zhang, X.; Hou, B.; Wang, L. Constructing heterojunctions of CoAl2O4 and Ni3S2 anchored on carbon cloth to acquire multiple active sites for efficient overall water splitting. J. Electroanal. Chem. 2024, 956, 118109. [Google Scholar] [CrossRef]
  44. Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169–11186. [Google Scholar] [CrossRef] [PubMed]
  45. Rajagopal, A.K.; Callaway, J. Inhomogeneous electron gas. Phys. Rev. B 1964, 136, 3B865. [Google Scholar] [CrossRef]
  46. Kohn, W.; Sham, L. Self-consistent equations including exchange and correlation effects. Phys. Rev. B 1965, 140, A1133. [Google Scholar] [CrossRef]
  47. Perdew, J.P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865–3868. [Google Scholar] [CrossRef]
  48. Perdew, J.P.; Chevary, J.A.; Vosko, S.H.; Jackson, K.A.; Pederson, M.R.; Singh, D.J.; Fiolhais, C. Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B 1992, 46, 6671–6687. [Google Scholar] [CrossRef]
  49. Luo, Y.; Li, X.; Cai, X.; Zou, X.; Kang, F.; Cheng, H.M.; Liu, B. Two-dimensional MoS2 Confined Co(OH)2 Electrocatalysts for hydrogen evolution in alkaline electrolytes. ACS Nano 2018, 12, 4565–4573. [Google Scholar] [CrossRef]
Catalysts 14 00664 g001
Figure 1. The XRD patterns of CC (a), CGOx samples (b), and CGOx@CC samples (c); the comparison between the synthetic CGO36 sample and the calculation results of the standard crystal model (insert picture) (d).
Figure 1. The XRD patterns of CC (a), CGOx samples (b), and CGOx@CC samples (c); the comparison between the synthetic CGO36 sample and the calculation results of the standard crystal model (insert picture) (d).
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Figure 2. The SEM morphology of CC (a), CGO18@CC (b), CGO24@CC (c), and CGO36@CC (d,e) materials; EDX mapping (f) of analysis area of 4e; the schematic diagram of the theoretical process of Co2GeO4 crystal formation (g).
Figure 2. The SEM morphology of CC (a), CGO18@CC (b), CGO24@CC (c), and CGO36@CC (d,e) materials; EDX mapping (f) of analysis area of 4e; the schematic diagram of the theoretical process of Co2GeO4 crystal formation (g).
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Figure 3. The XPS full spectrum scanning of all CGOx@CC composites (a) and the high-resolution XPS results of Co 2p (b), Ge 3d (c), and O 1s (d) of CGO18@CC, CGO24@CC, and CGO36@CC composites.
Figure 3. The XPS full spectrum scanning of all CGOx@CC composites (a) and the high-resolution XPS results of Co 2p (b), Ge 3d (c), and O 1s (d) of CGO18@CC, CGO24@CC, and CGO36@CC composites.
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Figure 4. The CV curves of the non-Faraday region (different scanning speeds) ((a): carbon cloth, (b): CGO18@CC, (c): CGO24@CC, and (d): CGO36@CC); plots of capacitive current density vs. different scan rate for Cdl (e).
Figure 4. The CV curves of the non-Faraday region (different scanning speeds) ((a): carbon cloth, (b): CGO18@CC, (c): CGO24@CC, and (d): CGO36@CC); plots of capacitive current density vs. different scan rate for Cdl (e).
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Figure 5. The HER IR-corrected LSV polarization curves (a,b) (detail), Tafel plots (c), and EIS spectra (d) of Carbon cloth, CGO18@CC, CGO24@CC, and CGO36@CC composites (the insert picture is analog circuit).
Figure 5. The HER IR-corrected LSV polarization curves (a,b) (detail), Tafel plots (c), and EIS spectra (d) of Carbon cloth, CGO18@CC, CGO24@CC, and CGO36@CC composites (the insert picture is analog circuit).
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Figure 6. (a) The i-t-test of the CGO36@CC composite for 100 h at a HER potential of 100, 196, 246, and 281 mV (25 h for each); (b) LSV polarization curves before and after the stability test of 5000 CV cycles; XRD patterns (c), and high-resolution XPS results of Co 2p (d), Ge 3d (e), and O1s (f) of CGO36@CC before and after the stability testing.
Figure 6. (a) The i-t-test of the CGO36@CC composite for 100 h at a HER potential of 100, 196, 246, and 281 mV (25 h for each); (b) LSV polarization curves before and after the stability test of 5000 CV cycles; XRD patterns (c), and high-resolution XPS results of Co 2p (d), Ge 3d (e), and O1s (f) of CGO36@CC before and after the stability testing.
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Figure 7. The synthesis process of CGOx and CGOx@CC samples (x is the hydrothermal reaction time).
Figure 7. The synthesis process of CGOx and CGOx@CC samples (x is the hydrothermal reaction time).
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Table 1. The electrochemistry HER performance of recent cobalt-related electrocatalytic materials.
Table 1. The electrochemistry HER performance of recent cobalt-related electrocatalytic materials.
CatalystHER Overpotential
(mV at 10 mA·cm−2)		HER Tafel Slope (mV dec−1)References
Co3O4@MoO3158148[4]
Co SAs-Co NPs/NCFs20583.2[30]
CoMo2S45584.61[31]
Pt/Nb-Co(OH)211282[32]
Co/Mo2C@C9868[33]
Co-Co2C/CC9682.2[34]
Co/CoO@NC@CC15280[21]
Co/CoP@PNC-1013789.8[35]
Co(OH)2/Fe7Se8183116[36]
CoP@CoP@(Co/Ni)2P14772.7[37]
Fe–Co-O/Co@NC-mNS/NF11296[38]
CoSe/Co(OH)2-CM (AE)207126[39]
Co2GeO4 loaded on Ni Foam16579[27]
CGO36@CC sample9548.9This work
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Chen, C.; Zhu, J.; Cheng, T.; Wu, F.; Xie, J.; He, D.; Dai, Y.; Zhang, X.; Zhao, L.; Wei, Z. Accelerated Electrons Transfer and Synergistic Interplay of Co and Ge Atoms (111 Crystal Plane) Activated by Anchoring Nano Spinel Structure Co2GeO4 onto Carbon Cloth Composite Electrocatalyst for Highly Enhanced Hydrogen Evolution Reaction. Catalysts 2024, 14, 664. https://doi.org/10.3390/catal14100664

AMA Style

Chen C, Zhu J, Cheng T, Wu F, Xie J, He D, Dai Y, Zhang X, Zhao L, Wei Z. Accelerated Electrons Transfer and Synergistic Interplay of Co and Ge Atoms (111 Crystal Plane) Activated by Anchoring Nano Spinel Structure Co2GeO4 onto Carbon Cloth Composite Electrocatalyst for Highly Enhanced Hydrogen Evolution Reaction. Catalysts. 2024; 14(10):664. https://doi.org/10.3390/catal14100664

Chicago/Turabian Style

Chen, Chen, Jiarui Zhu, Ting Cheng, Fei Wu, Jun Xie, Dawei He, Youzhi Dai, Xiao Zhang, Le Zhao, and Zhongsheng Wei. 2024. "Accelerated Electrons Transfer and Synergistic Interplay of Co and Ge Atoms (111 Crystal Plane) Activated by Anchoring Nano Spinel Structure Co2GeO4 onto Carbon Cloth Composite Electrocatalyst for Highly Enhanced Hydrogen Evolution Reaction" Catalysts 14, no. 10: 664. https://doi.org/10.3390/catal14100664

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