**1. Introduction**

Blockchain was first proposed as Bitcoin's distributed ledger to alleviate the doublespending problem. One of the most important characteristics of blockchain is that, due to its transparency and immutability, it enables participants to establish trust among unknown entities in a decentralized way [1,2]. Recently, in the area of smart mobility, blockchain has risen as an upcoming technology, enabling decentralized mobility services, secure and reliable P2P energy trading between EVs, secure authentication and more [3]. According to Markets and Markets [4], by 2030, the automotive blockchain market is expected to have grown from USD 0.35 billion in 2020 to USD 5.29 billion, drawing the attention of a variety of stakeholders (e.g., investors, business experts, academics and governments).

Additionally, cities are becoming smarter and more connected, due to the rapid advancement of the Internet of Things (IoT). IoT allows connected vehicles (e.g., electric vehicles) to gradually evolve into self-driving vehicles, but none of this will be feasible without a new advanced network [5]. Thus, IoV has emerged as technology that allows vehicle information exchange, efficiency and safety with each other. IoV is powered by smart vehicles, Artificial Intelligence and IoT [6,7]. In the context of IoV, smart vehicles use the Internet to communicate with each other and connect with drivers or passengers, as well as with roadside facilities [8]. The most important communication examples are Vehicle-to-Vehicle (V2V) and Vehicle-to-Grid (V2G) [9].

**Citation:** Kapassa, E.;

Themistocleous, M. Blockchain Technology Applied in IoV Demand Response Management: A Systematic Literature Review. *Future Internet* **2022**, *14*, 136. https://doi.org/ 10.3390/fi14050136

Academic Editors: Ahad ZareRavasan, Taha Mansouri, Michal Krˇcál, Saeed Rouhani and Paolo Bellavista

Received: 14 March 2022 Accepted: 27 April 2022 Published: 29 April 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Yet, the widespread utilization of dispersed EVs creates problems for the energy managemen<sup>t</sup> in IoV [10,11]. A possible solution is DR management, which might be used in IoV to allow energy consumers (i.e., EV drivers) to adjust their energy consumption patterns based on the cost [12,13]. Specifically, DR allows customers to play an important part in the energy grid operation by decreasing or changing their power usage during peak hours in response to time-based tariffs or other types of financial incentives. Several electric system operators utilize DR programs as alternatives for balancing supply and demand [14]. Such programs can reduce the cost of electricity in energy markets, resulting in reduced market prices. Time-based pricing schemes, including critical peak, variable peak, time of use and real-time pricing, are examples of how market players might participate in demand response [15,16].

Nevertheless, research in the area of IoV DR is still in its early stages and the deployment of IoV DR in smart grids confronts a number of important challenges [17,18]. Specifically, IoV currently lacks sufficient security and privacy procedures to reduce inaccurate and malicious information transfers between EVs [19,20]. There is also a lack of incentive mechanisms to encourage prosumers (i.e., producer and consumer) to join in such DR schemes. EV owners are hesitant to join in large-scale trading networks unless they are highly compensated (i.e., incentivization schemes), due to higher battery drain and other costs associated with discharging [21,22]. Additionally, IoV's characteristics, such as high mobility, low latency, network complexity and heterogeneity, pose substantial issues when typical cloud-based storage and managemen<sup>t</sup> is incorporated. As a result, to be ready for the future expansion of IoV and fulfill its potential, the data interchange and storage infrastructure may be distributed, decentralized, interoperable, adaptable and scalable [23–26].

From a different point of view, blockchain can be seen as a promising technology in the area of smart mobility and EVs, as it can support secure, reliable and decentralized energy trading [3,27,28]. Blockchain technology provides transparency regarding energy production and consumption. Moreover, blockchain has the potential to give a considerable number of unique solutions in the majority of IoV applications [6]. For that reason, researchers have started developing IoV applications based on blockchain technology [29–31]. IoV built on blockchain has the capacity to boost a new ecosystem for the transportation and vehicular industries, allowing energy assets to be transferred and managed in a secure, transparent, verifiable and efficient manner [32–34].

Despite the fact that IoV is a relatively new technology, it is known that decentralized designs and processes are required to manage energy generation and consumption. Based on our research findings presented in [6], instability in energy production may jeopardize the energy supply security, leading to energy overload and a greatly distributed and continuously changing IoV topology. As a result, we concluded that more study into DR management, which uses blockchain technology to balance energy consumption and supply, was required. In this regard, blockchain appears to have the potential to be an innovative paradigm, addressing limitations in IoV, such as variability in energy production, energy overload and lack of incentive mechanisms [6]. Even though there are several studies that investigate the blockchain technology in the energy domain, there is limited information regarding how blockchain could be incorporated in DR managemen<sup>t</sup> schemes designed for IoV. Therefore, there is a need to collect and critically analyze the existing literature in an attempt to highlight open issues. Thus, in this article, we conduct a SLR, investigating how blockchain technology assists the area of DRM in IoV. We contribute to the body of knowledge by offering a set of observations and research challenges on blockchain-based DRM in IoV, as the outcome of addressing the following SLR Question: "*How can blockchain technology assist the area of demand response management in IoV-assisted smart grids?*".

To this end, our study makes the following contributions based on a systematic literature review methodology:

1. Collects and filters the available literature, in an attempt to present current perspectives and research efforts on blockchain-enabled DRM in IoV.


The rest of this article is structured as follows. Section 2 provides a description of the followed research methodology of the current review, describing step by step the three stages of this articles, based on Kitchenham's approach [35,36], as well as features of the PRISMA methodology [37]. Then, Section 3 presents the main findings and the knowledge extracted during the review around current perspectives and research efforts on blockchainenabled DRM in IoV, while in Section 4, we critically discuss their findings, providing their main observations, as well as some limitations and research gaps. Finally, Section 5 concludes the paper, highlights its contributions and makes recommendations for further research. Lastly, we would like to mention that we provide a detailed list of abbreviations, in an attempt to ease the understanding of the concepts presented in this article.
