Advances on multi-heteroatom doped carbon catalysts: Synthesis, mechanistic insight, synergies, and application in microbial electrochemical energy, fuel and chemical production

Multi-heteroatom doping strategy emerged as a promising approach to overcome the limitations of carbon electrocatalysts through providing synergistic effects to tune electronic structures, increase/optimize active sites, improve stability, enhance biocompatibility and conductivity. This review provides a comprehensive analysis on progress in multi-heteroatom doped carbon electrocatalysts in microbial electrochemical technologies (METs) for wastewater treatment toward power generation, biohydrogen production, and CO 2 valorization through microbial fuel cells (MFCs), microbial electrolysis cells (MECs), and microbial electrosynthesis (MESs) respectively. Initially, the synthesis strategies from template-free pyrolysis and templating methods to advance MOF-derived and self-sacrificial routes were briefly summarized. Following, mechanistic insights by focusing on integration of advanced theoretical calculations and operando characterizations to understand how multi-doping tailor adsorption energies, charge redistribution, and intermediate stabilization in key electrocatalytic reactions such as the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and CO 2 reduction reaction (CO 2 RR) were thoroughly elucidated. Importantly, the structure–function relationships that link dopant type, coordination environment, and defect engineering with catalytic activity, durability, and selectivity were further elaborated. Finally, the current challenges and future research directions for designing advanced high-performance electrocatalysts toward sustainable practical METs were suggested. • State-of-the-art on multi-heteroatoms doped catalysts for key catalytic reactions in MET • Highlighting synthesis and operando techniques for multiple heteroatom catalysts • Examining synergies and trade-offs of metal/non-metal dopants in MET catalyst design • Extensive research focused on MFC while limited studies conduct on MEC and MES • Current challenges and future directions for MET catalyst research highlighted