Effect of hydrogen sources toward the CO2 photoreduction on boron decorated crystalline carbon nitride

[Display omitted] •Reaction mechanisms of two modes of Boron on PTI (Bi/PTI and Bs/PTI) for CO2 reduction are studied by DFT calculations.•In Bi/PTI, Bi is sp3 hybridized and follows the “acceptance-donation” process in adsorbing CO2, following a quasi-MvK mechanism for CO2 reduction.•In Bs/PTI, Lewis acid-base pairs make pyridine N as an active site and the reaction follows the adsorbed H* mechanism. Photocatalytic CO2 conversion to industrial fuels is considered an effective measure to solve energy and environmental problems. Presently, Catalysts for CO2 reduction reaction (CO2RR) are mostly confined to metal-based materials, but non-metal materials are less explored. We decorate the highly crystalline carbon nitride, i.e., poly(triazine) imides (PTI), with non-metallic boron (B) to obtain two B/PTI catalysts: Bi/PTI with B being deposited into the six-fold cavity of the PTI, and Bs/PTI with B substituting for C in PTI. For CO2RR, Bi/PTI follows a quasi Mars-van Krevelen process, but the high exposure of Bi results in an overly strong interaction with intermediates, inhibiting the reactivity. In contrast, Bs/PTI enhances the binding with intermediates by introducing Lewis acid-base pairs (B-N), which reduce the ring conjugation effect and induce the enrichment of electrons at the pyridine N. Hence, CO2 reduction with the adsorbed H* (Ha) hydrogenation mechanism in Bs/PTI has a significant reactivity.