Defect-Promoted Reductive Regeneration on Cobalt Catalysts Enables Efficient Dual-Pathway Hydrazine Electrooxidation

Hydrazine oxidation reaction (HzOR) represents a promising low-energy pathway for sustainable hydrogen production, yet mechanistic ambiguities and catalyst instability hinder its practical implementation. Herein, we elucidate the dual-pathway nature of HzOR on cobalt-based catalysts, involving direct electrooxidation on metallic Co and mediated oxidation via the redox cycle between metallic Co and cobalt hydroxide species. This mechanistic insight moves beyond the traditional focus on solely enhancing the intrinsic activity in the direct pathway. Instead, it highlights the chemical redox reaction between hydrazine and Co(II) as a central process that not only regenerates metallic Co sites for direct pathway but also drives the mediated oxidation route. Guided by this understanding, we designed a defect-rich cobalt catalyst through a one-step electrodeposition method, enabling fast chemical reduction of oxidized Co species by hydrazine. As a result, the catalyst delivers superior HzOR performance, reaching a current density of 100 mA cm^-2 at only -79 mV versus reversible hydrogen electrode, along with outstanding long-term stability. Combined electrochemical and density functional theory (DFT) analyses reveal that defect engineering significantly promotes the dual-pathway HzOR on Co-based catalysts. This work provides mechanistic understanding of HzOR electrocatalysis and highlights a general strategy for designing efficient, durable non-noble metal electrocatalysts.