Abstract
Formic acid (HCOOH) electroreduction is poorly studied, even though it holds promise for energy conversion and storage applications. We use density functional theory to investigate the most likely products after four HCOOH electroreduction steps on Cu(111), Au(111), Ag(111), Zn(111), Pt(111), Pd(111), and Ru(111). On Cu(111), the formation of H(2), CO (and/or CO-derived C(2) products), CH(3)OH, and CH(4) is thermodynamically allowed. The Cu(111) surface has low selectivity because HCOOH reduction intermediates can adsorb via both O and C atoms. Experimentally, formic acid reduction on Cu produces H(2), C(2) products, and CH(3)OH, but very little CH(4). Interestingly, CO/CO(2) reduction on Cu produces CH(4) rather than CH(3)OH. The CO/CO(2) reduction pathway can proceed via the *COH intermediate, whereas HCOOH reduction can only proceed via the *CHO or CH(2)O*OH intermediates, possibly explaining the different product distribution. Au(111) is the most promising catalyst with high suggested selectivity to methanol and low hydrogen evolution rates. Ag(111) could be selective to methanol, but the first reduction step is very costly, so the reaction rates will be low. Zn(111), most likely, reduces HCOOH to CH(4), whereas Pt(111), Pd(111), and Ru(111) most likely produce CO poisoning the catalyst surfaces.