2D carbon nitrides: Regulating non-metal boron-doped C3N5 for elucidating the mechanism of wide pH range photocatalytic hydrogen evolution reaction

Solar-driven water splitting for green hydrogen production has been prospected as an auspicious technology to achieve sustainable energy generation by shifting towards renewable and zero-carbon emission fuels. Recently, N-rich C3N5 allotropes are emerging to surpass the intrinsic drawbacks of g-C3N4, which are the rapid recombination of photogenerated charge carriers and poor visible light absorption, resulting in low photocatalytic efficiency. In this study, density functional theory calculation was conducted on the pristine C3N5 and boron-doped C3N5 systems to study the effect of boron atom on the electronic and optical properties, as well as the hydrogen evolution reaction mechanism. The boron-dopants were introduced in C3N5 through substitutional or interstitial doping. It is indicated that the incorporation of boron atoms in the C3N5 matrix is thermodynamically favorable. A band gap narrowing of 0.6 eV was observed after the N3-site nitrogen atom was replaced by a boron atom (BN3-C3N5). Compared to pristine C3N5, the boron-dopant also reduced the reaction energies of potential determining step of the HER pathway in both acid and alkaline media through the Volmer-Tafel and Volmer-Heyrovsky mechanism. The Gibbs free energy of hydrogen adsorption (ΔGH*) of BN3-C3N5 (0.11 eV) is comparable to the benchmark Pt/C catalyst (–0.09 eV). These theoretical results allude to the elucidated catalytic performance of non-metal doped carbon nitrides that can be applied to future experimental and computational analysis.