Sustainable and selective formic acid production from photoelectrochemical methanol reforming at near-neutral pH using nanoporous nickel-iron oxyhydroxide-borate as the electrocatalyst

Industrial production of formic acid requires a highly energy-intensive process involving carbonylation of methanol with fossil fuel-based CO to methyl formate and subsequent hydrolysis of methyl formate to formic acid. In this study, we present a sustainable and selective production of formic acid from methanol-reforming using electro-synthesized nanoporous nickel-iron oxyhydroxide-borate thin film (nanoFe:Ni-Bi) as the electrocatalyst at near-neutral pH. We found that the incorporation of a suitable amount of iron not only facilitated the formation of active Ni³⁺ species but also improved the kinetics of methanol oxidation with active Ni³⁺ species, resulting in the significant enhancement in the formate production. Notably, nanoFe:Ni-Bi with optimal Fe content exhibited a turnover frequency (TOF) of 152.71 ± 9.95 h⁻¹ with Faradic efficiency for formate production (FE_formate) of 66.3 ± 1.7%, whereas nanoporous nickel oxyhydroxide-borate only showed a TOF of 56.65 ± 12.68 h⁻¹ with FE_formate of 30.5 ± 5.6%. In addition, a highly efficient and selective photoelectrochemical methanol-reforming system using nanoFe:Ni-Bi modified BiVO₄ photoanode was established. In contrast to the negligible activity of the pristine BiVO₄ photoanode, nanoFe:Ni-Bi modified BiVO₄ photoanode exhibited formate production rate of 5.7 ± 1.0 μmole cm⁻²h⁻¹ with a FE_formate of 94.6 ± 12.3% at an applied potential of 0.55 V vs. RHE under light illumination. This study provides a sustainable and less-energy intensive alternative route for the production of formic acid.