Investigation of Concerted Proton–Electron Donors for Promoting the Selective Production of HCOOH in CO2 Photoreduction

Achieving carbon neutralization by CO2 photoreduction (CO2PR) has attracted extensive attention. However, limited selectivity and harsh reaction conditions impede its practical application. Herein, we introduced a hydrogen storage material, ammonia borane (NH3BH3, AB), as mild proton–electron pair (adsorbed H atom, *H) donors, to realize synergistic hydrogen evolution and selective photocatalytic CO2 reduction to HCOOH. A preeminent HCOOH generation rate of 5237.8 μmol g–1 h–1 (with a HCOOH selectivity of 99.67% in carbonaceous products) was obtained. Intriguingly, *H provided by AB could accelerate selective HCOOH generation over Cu2O/TiO2 by promoting intermediate *HCOO generation in kinetics, and AB adsorption on Cu/TiO2 surface could also reduce the activation energy of HCOOH production in thermodynamics. Furthermore, some other similar *H donors have performed equally well in selective HCOOH, thus providing guidance for the design of a high-performance CO2PR system over the consideration of *H protons to meet the demand of sustainable development in the future.