Research

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15 pages, 2825 KiB

Open AccessArticle

Oxygen Reduction Reaction and Hydrogen Evolution Reaction Catalyzed by Pd–Ru Nanoparticles Encapsulated in Porous Carbon Nanosheets

by Juntai Tian, Wen Wu, Zhenghua Tang, Yuan Wu, Robert Burns, Brandon Tichnell, Zhen Liu and Shaowei Chen

Catalysts 2018, 8(8), 329; https://doi.org/10.3390/catal8080329 - 11 Aug 2018

Cited by 47 | Viewed by 7228

Abstract

Developing bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for enhancing the energy transfer efficiency of metal–air batteries and fuel cells, as well as producing hydrogen with a high purity. Herein, a series of Pd–Ru alloyed [...] Read more.

Developing bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for enhancing the energy transfer efficiency of metal–air batteries and fuel cells, as well as producing hydrogen with a high purity. Herein, a series of Pd–Ru alloyed nanoparticles encapsulated in porous carbon nanosheets (CNs) were synthesized and employed as a bifunctional electrocatalyst for both ORR and HER. The TEM measurements showed that Pd–Ru nanoparticles, with a size of approximately 1–5 nm, were uniformly dispersed on the carbon nanosheets. The crystal and electronic structures of the Pd_xRu_100−x/CNs series were revealed by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The as-prepared samples exhibited effective ORR activity in alkaline media and excellent HER activity in both alkaline and acid solutions. The Pd₅₀Ru₅₀/CNs sample displayed the best activity and stability among the series, which is comparable and superior to that of commercial 10% Pd/C. For ORR, the Pd₅₀Ru₅₀/CNs catalyst exhibited an onset potential of 0.903 V vs. RHE (Reversible Hydrogen Electrode) and 11.4% decrease of the current density after 30,000 s of continuous operation in stability test. For HER, the Pd₅₀Ru₅₀/CNs catalyst displayed an overpotential of 37.3 mV and 45.1 mV at 10 mA cm⁻² in 0.1 M KOH and 0.5 M H₂SO₄, respectively. The strategy for encapsulating bimetallic alloys within porous carbon materials is promising for fabricating sustainable energy toward electrocatalysts with multiple electrocatalytic activities for energy related applications. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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14 pages, 5595 KiB

Open AccessArticle

Influence of Transition Metal on the Hydrogen Evolution Reaction over Nano-Molybdenum-Carbide Catalyst

by Meng Chen, Yufei Ma, Yanqiang Zhou, Changqing Liu, Yanlin Qin, Yanxiong Fang, Guoqing Guan, Xiumin Li, Zhaoshun Zhang and Tiejun Wang

Catalysts 2018, 8(7), 294; https://doi.org/10.3390/catal8070294 - 22 Jul 2018

Cited by 34 | Viewed by 7199

Abstract

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor [...] Read more.

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the β-Mo₂C phase was formed in all metal-doped samples. X-ray photoelectron spectroscopy analysis indicated that the binding energy of Mo²⁺ species (Mo₂C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure β-Mo₂C, the electrocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-Mo₂C). The 2% Pt-Mo₂C required a η₁₀ of 79 mV, and outperformed that of pure β-Mo₂C (η₁₀ = 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpotential (32 mV) in 0.5 M H₂SO₄. Also, the 2% Pt-Mo₂C catalyst demonstrated a high stability for the HER in 0.5 M H₂SO₄. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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13 pages, 5185 KiB

Open AccessArticle

An Iron-Based Catalyst with Multiple Active Components Synergetically Improved Electrochemical Performance for Oxygen Reduction Reaction

by Jian Zhang, Xiaoming Song, Ping Li, Shuai Wang, Zexing Wu and Xien Liu

Catalysts 2018, 8(6), 243; https://doi.org/10.3390/catal8060243 - 07 Jun 2018

Cited by 5 | Viewed by 4194

Abstract

Lack of highly active and stable non-precious metal catalysts (NPMCs) as an alternative to Pt for oxygen reduction reaction (ORR) in the application of zinc-air batteries and proton-exchange membrane fuel cells (PEMFCs) significantly hinders the commercialization of these energy devices. Herein, we synthesize [...] Read more.

Lack of highly active and stable non-precious metal catalysts (NPMCs) as an alternative to Pt for oxygen reduction reaction (ORR) in the application of zinc-air batteries and proton-exchange membrane fuel cells (PEMFCs) significantly hinders the commercialization of these energy devices. Herein, we synthesize a new type of catalyst composed of nitrogen-coordinated and carbon-embedded metal (Fe-N/Fe₃C/Fe/C) by pyrolyzing a precursor at 800 °C under argon atmosphere, and the precursor is obtained by heating a mixture of the tri (dipyrido [3,2-a:2′,3′-c] phenazinyl) phenylene and FeSO₄ at 160 °C in a Teflon-lined stainless autoclave. The resultant Fe-N/Fe₃C/Fe/C-800 exhibits the highest activity for the ORR with onset and half-wave potentials of 1.00 and 0.82 V in 0.1 M KOH, respectively. Furthermore, it also shows a potential ORR activity in 0.1 M HClO₄, which is promising for the application in commercial PEMFCs. Most importantly, Fe-N/Fe₃C/Fe/C-800 exhibits a comparable electrochemical performance to Pt/C for the application in zinc-air battery. The specific capacity approaches 700 mAh·g⁻¹, and the maximum power density is also comparable to that of Pt/C at the current density of 200 mA·cm⁻². The work opens up a simple strategy to prepare ORR electrocatalyts for zinc-air battery and PEMFCs. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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14 pages, 7139 KiB

Open AccessArticle

Electrocatalytic Performance of Carbon Supported WO₃-Containing Pd–W Nanoalloys for Oxygen Reduction Reaction in Alkaline Media

by Nan Cui, Wenpeng Li, Zengfeng Guo, Xun Xu and Hongxia Zhao

Catalysts 2018, 8(6), 225; https://doi.org/10.3390/catal8060225 - 24 May 2018

Cited by 10 | Viewed by 4333

Abstract

In this paper, we report that WO_x containing nanoalloys exhibit stable electrocatalytic performance in alkaline media, though bulk WO₃ is easy to dissolve in NaOH solution. Carbon supported oxide-rich Pd–W alloy nanoparticles (PdW/C) with different Pd:W atom ratios were prepared by [...] Read more.

In this paper, we report that WO_x containing nanoalloys exhibit stable electrocatalytic performance in alkaline media, though bulk WO₃ is easy to dissolve in NaOH solution. Carbon supported oxide-rich Pd–W alloy nanoparticles (PdW/C) with different Pd:W atom ratios were prepared by the reduction–oxidation method. Among the catalysts, the oxide-rich Pd_0.8W_0.2/C (Pd/W = 8:2, atom ratio) exhibits the highest catalytic activity for the oxygen reduction reaction. The X-ray photoelectron spectroscopy data shows that ~40% of Pd atoms and ~60% of the W atoms are in their oxide form. The Pd 3d_5/2 binding energy of the oxide-rich Pd–W nanoalloys is higher than that of Pd/C, indicating the electronic structure of Pd is affected by the strong interaction between Pd and W/WO₃. Compare to Pd/C, the onset potential of the oxygen reduction reaction at the oxide-rich Pd_0.8W_0.2/C shifts to a higher potential. The current density (mA·mg Pd⁻¹) at the oxide-rich Pd_0.8W_0.2/C is ~1.6 times of that at Pd/C. The oxide-rich Pd_0.8W_0.2/C also exhibits higher catalytic stability than Pd/C, which demonstrates that it is a prospective candidate for the cathode of fuel cells operating with alkaline electrolyte. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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15 pages, 3954 KiB

Open AccessArticle

Cost-Effective and Facile Preparation of Fe₂O₃ Nanoparticles Decorated N-Doped Mesoporous Carbon Materials: Transforming Mulberry Leaf into a Highly Active Electrocatalyst for Oxygen Reduction Reactions

by Tingting Zhang, Lihao Guan, Changqing Li, Junfeng Zhao, Manchao Wang, Lin Peng, Jiahui Wang and Yuqing Lin

Catalysts 2018, 8(3), 101; https://doi.org/10.3390/catal8030101 - 28 Feb 2018

Cited by 14 | Viewed by 5257

Abstract

Herein, a promising method to prepare efficient N-doped porous carbon-supported Fe₂O₃ nanoparticles (Fe₂O₃/N-PCs) ORR electrocatalysts is presented. The porous carbon was derived from a biomass i.e., mulberry leaf through a cost-effective approach. The existence of diverse [...] Read more.

Herein, a promising method to prepare efficient N-doped porous carbon-supported Fe₂O₃ nanoparticles (Fe₂O₃/N-PCs) ORR electrocatalysts is presented. The porous carbon was derived from a biomass i.e., mulberry leaf through a cost-effective approach. The existence of diverse compounds containing carbon, oxygen, nitrogen and sulfur in mulberry leaf benefit the formation and uniform dispersion of Fe₂O₃ nanoparticles (NPs) in the porous carbon. In evaluating the effects of the carbon support on the Fe₂O₃ NPs towards the ORR, we found that the sample of Fe₂O₃/N-PCs-850 (Fe₂O₃/N-PCs obtained at 850 °C) with high surface area of 313.8 m²·g⁻¹ exhibits remarkably superior ORR activity than that of materials acquired under other temperatures. To be specific, the onset potential and reduction peak potential of Fe₂O₃/N-PCs-850 towards ORR are 0.936 V and 0.776 V (vs. RHE), respectively. The calculated number of electron transfer n for the ORR is 3.9, demonstrating a near four-electron-transfer process. Furthermore, it demonstrates excellent longtime stability and resistance to methanol deactivation compared with Pt/C catalyst. This study provides a novel design of highly active ORR electrocatalysts from low-cost abundant plant products. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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12 pages, 5639 KiB

Open AccessArticle

Synthesis of Three-Dimensionally Ordered Macroporous NiCe Catalysts for Oxidative Dehydrogenation of Propane to Propene

by Kegong Fang, Lulu Liu, Mingwei Zhang, Lu Zhao, Juan Zhou, Wenbin Li, Xiaoliang Mu and Cheng Yang

Catalysts 2018, 8(1), 19; https://doi.org/10.3390/catal8010019 - 10 Jan 2018

Cited by 15 | Viewed by 4742

Abstract

Three-dimensionally ordered macroporous (3DOM) NiCe catalysts with different Ni/Ce molar ratio were fabricated using the colloidal crystal templating method. The physic-chemical properties of the samples were characterized by various techniques, including N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, and [...] Read more.

Three-dimensionally ordered macroporous (3DOM) NiCe catalysts with different Ni/Ce molar ratio were fabricated using the colloidal crystal templating method. The physic-chemical properties of the samples were characterized by various techniques, including N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, and H₂-temperature-programmed reduction (TPR) characterizations. The results revealed that the 3DOM NiCe samples preserved the three-dimensionally ordered macroporous channels with interlinked micro- or mesoporous structure and highly dispersed nickel oxide species in the framework upon different amount of nickel incorporation. In the evaluation of the oxidative dehydrogenation (ODH) of propane, the 3DOM NiCe catalysts exhibited higher selectivity and yield to propene than the amorphous NiCe catalyst. An optimum yield of propene of 11.9% with the 30.3% propane conversion at 375 °C was obtained over the 3DOM 2NiCe catalyst. Combining XRD, TPR, and Raman analysis, it could be found that the nickel incorporation in CeO₂ lattice produced a high concentration of oxygen vacancies that were the active sites for the oxidative dehydrogenation of propane. Besides this, the 3DOM structure promoted the rapid diffusion of the reactants and products—favorable for the generation of propene in the ODH of propane. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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Review

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16 pages, 7883 KiB

Open AccessReview

Probing Active Sites on Metal-Free, Nitrogen-Doped Carbons for Oxygen Electroreduction: A Review

by Ni Zhou, Nan Wang, Zexing Wu and Ligui Li

Catalysts 2018, 8(11), 509; https://doi.org/10.3390/catal8110509 - 01 Nov 2018

Cited by 61 | Viewed by 7889

Abstract

The Metal-free nitrogen-doped carbons represent an emerging low-cost nonprecious electrocatalyst for oxygen reduction reaction (ORR) that is a sluggish process at the cathode of polymer electrolyte membrane fuel cells (PEMFCs) and a verity of metal-air batteries. During the past few years, the ORR [...] Read more.

The Metal-free nitrogen-doped carbons represent an emerging low-cost nonprecious electrocatalyst for oxygen reduction reaction (ORR) that is a sluggish process at the cathode of polymer electrolyte membrane fuel cells (PEMFCs) and a verity of metal-air batteries. During the past few years, the ORR catalytic activity of nitrogen-doped carbons has been significantly increased, making them highly competitive alternatives to conventional precious metals based electrocatalysts for ORR. However, controversies remain in the unambiguous identification of the ORR active sites on nitrogen-doped carbons. This review summarizes the recent progress in probing the potential active sites on metal-free nitrogen-doped carbons for ORR, aiming to gain in-depth understanding of the ORR catalytic mechanism on nitrogen-doped carbons for further enhancing ORR activity. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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17 pages, 2035 KiB

Open AccessReview

Recent Progress in Nitrogen-Doped Metal-Free Electrocatalysts for Oxygen Reduction Reaction

by Zexing Wu, Min Song, Jie Wang and Xien Liu

Catalysts 2018, 8(5), 196; https://doi.org/10.3390/catal8050196 - 07 May 2018

Cited by 66 | Viewed by 7120

Abstract

Electrocatalysis for the oxygen reduction reaction (ORR) at the cathode plays a critical role in fuel cells and metal-air batteries. However, the high-cost and sluggish kinetics of the catalytic reaction have hindered its development. Therefore, developing efficient catalysts to address these issues is [...] Read more.

Electrocatalysis for the oxygen reduction reaction (ORR) at the cathode plays a critical role in fuel cells and metal-air batteries. However, the high-cost and sluggish kinetics of the catalytic reaction have hindered its development. Therefore, developing efficient catalysts to address these issues is of vital significance. In this work, we summarized the recent progress of nitrogen (N)-doped metal-free catalysts for the ORR, owing to their high catalytic activity (comparable to Pt/C) and cost-effectiveness. The synthetic strategy and the morphology structure to catalytic performance are mainly discussed. Furthermore, the design of N-doped nanomaterials with other heteroatoms in aiming to further enhance the ORR performance is also reviewed. At the end of the review, we provide a brief summary of the N-doped carbon-based catalysts in enhancing the ORR performance and give future perspectives for their further development. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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18 pages, 2723 KiB

Open AccessReview

Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

by Zhenghua Tang, Wen Wu and Kai Wang

Catalysts 2018, 8(2), 65; https://doi.org/10.3390/catal8020065 - 07 Feb 2018

Cited by 62 | Viewed by 10331

Abstract

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. [...] Read more.

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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