Mechanochemistry: Fundamentals, applications and future

A concept of template-assisted mechanosynthesis for solid-state production of bifunctional Fe-N-C oxygen electrocatalyst Akmal Kosimov 1 , Amina Alimbekova 1 , Jürgen-Martin Assafrei 1 , Gulnara Yusibova 1 , Jaan Aruväli 2 , Majid Ahmadi 3 , Khatereh Roohi 4 , Peyman Taheri 4 and Nadežda Kongi 1 1 Institute of Chemistry, University of Tartu, Estonia, 2 Institute of Ecology and Earth Sciences, University of Tartu, Estonia, 3 Zernike Institute for Advanced Materials, University of Groningen, Netherlands, 4 Department of Materials Science and Engineering, Delft University of Technology, Netherlands The energy crisis of recent years accelerated the plans for the transition toward renewable energy alternatives. These technologies are typically held to a higher standard since they must be secure, sustainable, cost-effective, and efficient. 1 However, renewable energy lacks security as its supply is not always continuous and may not fulfill the demands. 2 Therefore, there is a need for an agile technology to convert and store the incoming energy smartly. Fuel cells and metal-air batteries are potential solutions for next-generation electrochemical energy conversion and storage yet they remain heavily reliant on Pt-group metals (PGMs) to effectively overcome the overpotentials of oxygen reduction/evolution reactions. The utilization of PGMs inevitably leads to high costs and poor stability, therefore making it vital to find a substitute for the high-priced PGMs.Among the recently developed materials, transition metals-based catalysts strike as desirable alternatives to PGMs owing to their low cost and a wide range of sources. In particular, the Metal/Nitrogen-doped Carbon-type (M-N-C) materials demonstrate outstanding catalytic activity and exceptional stability. Despite their activity, the large-scale production of M-N-C-type materials still poses a challenge since most of the currently employed methods are solution-based and raise many issues concerning sustainability: toxic/ hazardous waste formation, time/energy expenses, excessive solvent use, and overall compliance with current environmental requirements. M-N-C-type catalysts are typically made by doping/wet-impregnating carbon support with metal/nitrogen source followed by carbonization of the material. Alternatively, M-N-C materials can be formed by the synthesis of metal-organic species and their subsequent pyrolysis, which could be further investigated for possible mechanochemical production. Mechanosynthesis can potentially become a facile alternative for fabricating M-N-Cs that would mitigate the sustainability concerns and promote the industry-scale applications of the catalysts. Therefore, our research focuses on developing a reliable protocol of mechanosynthesis that employs a NaCl-templating agent to produce M-N-C catalysts. Here we propose a concept of a sustainable and cost-effective route for producing Fe-N-C-type catalysts with a bifunctional activity comparable to the state-of-the-art. The method combines mechanochemistry via liquid- assisted grinding/compression (LAG and LAC) and NaCl as a sacrificial templating agent. This study yielded a series of meso/microporous Fe- and N-doped carbon materials which exhibit high electrocatalytic efficiency, and a high degree of porosity. A proposed method opens new avenues for environmentally sustainable large-scale implementation of high-performance M-N-C catalysts for clean energy systems. References 1. Yana Popkostova, “EUROPE’S ENERGY CRISIS CONUNDRUM Origins, impact and way forward,” European Union Institute for Security Studies , Jan. 2022 . (https://www.iss.europa.eu/content/europes-energy-crisis-conundrum). 2. Ibrahim, A. Ilinca, and J. Perron, “Energy storage systems—Characteristics and comparisons,” Renew. Sustain. Energy Rev. , 2008 , vol. 12, no. 5, pp. 1221–1250, DOI: 10.1016/j.rser.2007.01.023.

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