Exclusive Formate Reaction Route over Pd/NiN₄Cl for High-Performance Formic Acid Oxidation

Direct formic acid fuel cells have emerged as promising energy conversion systems, with Pd being a leading candidate for the active center of formic acid oxidation reaction at the anode. However, the mass activity of Pd still falls short of meeting application demands. This work explores the adjustment effect of a unique NiN4Cl support for anchoring Pd NPs (Pd/NiN4Cl), preferentially promoting the formate pathway over the direct formic acid pathway. The Pd/NiN4Cl exhibits unexpected FAOR activity, with a mass activity 3.3 times and a specific activity 4.5 times higher than commercial Pd/C, and even a significant reduction in overpotential at 6 mA cm–2. Electrochemical in situ ATR-SEIRAS and density functional theory calculations reveal that the Pd/NiN4Cl significantly change reaction pathways to exclusive formate pathways, which mitigates the generation of CO* species. The crystal orbital overlap population diagram indicates that the moderate Pd–O bond strength for HCOO* on the Pd/NiN4Cl surface is crucial for the specificity of the FAOR pathway. Additionally, the synergistic interaction between NiN4Cl and Pd will efficiently oxidize any residual CO*. This work provides valuable insights into optimizing FAOR performance through creating novel support for tuning reaction pathways.