Bimetallic Pd-Based surface alloys promote electrochemical oxidation of formic acid: Mechanism, kinetics and descriptor

Abstract Palladium is well noted as anode catalyst for promoting electrochemical oxidation of formic acid (FAO) in direct formic acid fuel cell thanks to its high CO tolerance. Here, using combined approach of density-functional theory calculations and microkinetic modeling, we investigate the fundamental aspects of FAO catalyzed by bimetallic M@Pd(111) single-atom surface alloys (where M = Mo, Fe, Ru, Co, Ni, Cu, Zn, Ag, Au). Our results suggest that M@Pd(111) are highly stable and outperforms Pd(111) for FAO via primarily the direct mechanism: HCOOH → *HCOO (formate) → CO2 + 2H+ + 2e−. It is revealed that the decoordination of *HCOO from bidentate to monodentate adsorption mode (i.e., *bHuCOO → *mHdCOO) followed by the facile carbonyl-H abstraction forming CO2 + (H++e−) could be the potential-determining steps. Moreover, Mo@Pd(111) is predicted to be the most promising bimetallic Pd-based catalyst for FAO based on the weakest *CO binding and the strongest *OH binding with alloyed Mo, which therefore can be used as an effective descriptor for designing FAO catalysts with high activity. The simulated polarization curves of FAO on Pd(111) and Ru@Pd(111) agree reasonably well with the experiment, an indicative of the validity of mechanism and kinetics derived from this study.