Grain-Boundary Engineering for Electrocatalysis: From Precise Structural Analysis to Reaction-Pathway Regulation

Amid efforts toward carbon neutrality and rapid renewable energy development, CO₂/CO electroreduction and water electrolysis have emerged as critical pathways for carbon resource recycling and green hydrogen production. However, CO₂ and CO electroreduction reaction (CO₂RR/CORR) remain limited by complex multielectron-transfer pathways, insufficient product selectivity, and poor stability at high current densities. Meanwhile, the hydrogen and oxygen evolution reactions (HER/OER) face challenges associated with noble-metal dependence, sluggish kinetics, and structural instability. Grain boundaries are interfacial defects that can feature low-coordinated atoms, local strain, and reconstructed electronic structures, thus offering a promising platform for designing catalysts with enhanced activity, selectivity, and stability. This Review examines the fundamental concepts, classifications, and structure-activity relationships of grain boundaries. It further outlines synthesis strategies for grain-boundary-rich materials and discusses advanced characterization approaches ranging from morphological identification and GB quantification to in situ/operando tracking. The discussion subsequently focuses on the applications and catalytic mechanisms of grain boundaries in the CO₂RR, CORR, HER, and OER. Representative mechanisms involve regulating intermediate adsorption, promoting C-C coupling, optimizing charge transfer, stabilizing active valence states, and improving the reaction microenvironment. By integrating synthesis, characterization, catalytic applications, and mechanistic insights, this Review provides a theoretical framework for the precise design, mechanistic understanding, and practical deployment of grain-boundary-based catalysts.