Unconventional and scalable synthesis of non-precious metal electrocatalysts for practical proton exchange membrane and alkaline fuel cells: A solid-state co-ordination synthesis approach

Synthesis of non-precious metal catalysts (NPMC) has been gaining significant interest in recent years due to their low cost and excellent oxygen reduction reaction (ORR) activity. However, their successful entry into the real market had been challenged primarily by their ease of synthesis in large quantities, with a reproducible electrocatalytic activity. In this review, we comprehensively discussed the potentials of cathodic ORR catalysts synthesized by the "solvent-free, mechanochemical " approach, that can be extended to pilot scale synthesis to meet the commercial demand. Mechanochemical synthesis processes display simplicity and high reproducibility and versatility in synthesis of NPMC for ORR. The primary role of mechanical energy in the solid catalyst synthesis, the physicochemical, electrochemical properties and the fuel cell performance of synthesized catalysts by mechanochemical are discussed in this review. A number of extraordinary Fe and Co based catalysts have been synthesized by the solid-state, mechanochemical processes whose ORR activity and single cell performance are far more than the state-of-the-art Pt/C catalysts. We also systematically evaluated the effect of various solvent-free meth-ods, effect of various precursors used, morphology of the catalysts, M-x-N-y-C active sites on ORR. Interestingly, some reports also show gram scale synthesis, which we feel it's highly encouraging and justifying the significance of mechanochemical synthesis for industrial demands. This review recognizes, mechanochemical synthesis as an excellent and the best possible way to meet the industrial demands together with environmental sustainability. (c) 2022 Elsevier B.V. All rights reserved.