Hydrophilic Single-Atom Interface Empowered Pure Formic Acid Fuel Cells

Single-atom catalysts (SACs), offering high mass activity and enhanced resistance to poisoning, are regarded as superior alternatives to traditional Pt/Pd nanocatalysts for direct formic acid fuel cells (DFAFCs). However, failure toward operation in concentrated formic acid (FA), which is critical for portable electronics, challenges their antipoisoning advantage and highlights a missing part in the understanding of the reaction. We herein demonstrate that the interfacial hydrophilicity of SACs is pivotal for high-performance DFAFCs, enabling, for the first time, stable operation with pure FA (>99%). By incorporating transition metal single atoms (Co, Fe, Ni, Ru) into Ir/NC catalysts, we engineered highly hydrophilic interfaces, as validated by molecular dynamics simulations and experimental studies. The optimized IrCo/NC anode exhibited a mass activity 342 times higher than that of nanoparticle-based catalysts and represented as the first SAC to achieve a higher peak power density (107.7 mW cm^-2). A new reaction mechanism is revealed, where CO acts as a reactive intermediate rather than a poison. Further, in situ spectroscopy and isotope kinetic analyses identified water intermediate involvement in the rate-determining step, underscoring the critical role of hydrophilic interface engineering in DFAFC.