One Stone, Three Birds: Dual Hydrogen Production from Water Reduction and Formaldehyde Oxidation Predicted on Metal-free Electrocatalysts

Abstract

Due to the sluggish oxygen evolution reaction (OER) at the anode side, hydrogen generation by electrocatalytic water splitting is primarily hindered by its high voltage demand and low energy conversion efficiency. Here, using state-of-the-art first-principles calculations, we predict that the boron dimer (B₂)doping in g-C₃N₄/graphene heterostructure (B₂@C₃N₄/Gra) exhibits “one stone, three birds” functionality for efficient bipolar hydrogen production. Firstly, B₂@C₃N₄/Gra system displays remarkable catalytic activity for hydrogen production via hydrogen evolution reaction (HER) with ultra-low limiting potential, around 0.26 ~ 0.31 V, within the entire pH range at the cathode. Secondly, at the anode, an alternative formaldehyde oxidation reaction (FOR) process leads to a reduction of the limiting potential to 0.20 V for hydrogen generation, which is even superior to the noble-metal-based catalysts reported so far. Thirdly, the present strategy in dual H₂ production via the metal-free p-block elemental electrocatalyst is also valid to the introductions of other nonmetal elements with relatively low electronegativities, such as P, As, and Si. The underlying mechanism can be attributed to the synergetic effect of charge transfer and spin modulation induced by the “one stone”, i.e., B₂ doping, which effectively tunes the p-band center and the local spin state of the active sites of the plain pristine C₃N₄/Gra. These findings hold great promise for the design of high-efficient, cost-effective, and green p-block electrocatalysts in hydrogen generation.