A special Bi-S motif catalyst for highly selective CO2 conversion to methanol

Abstract

Carbon dioxide as raw materials chemically transformed to valuable, renewable and high-energetic carbon feedstocks, especially if driven by renewable energy, is a desirable way to mitigate the depletion of fossil fuels and allow environmentally neutral use of carbon fuels. However, it remains more exploration of electrocatalysts with high activity and superior selectivity in converting CO2 to storable carbon-based liquid fuels, like methanol. Herein, we develop an in-situ sulfurizing strategy over the Bi-based metal-organic frameworks (Bi-BTC) and disperse stable and special Bi-S motif on subsequent S-doped carbon-framework (called BS@Cx). Unlike the previous reports on Bi-based catalysts, as-prepared BS@Cx converted CO2 to methanol as major product at the whole applied potentials. Benefiting from the special Bi-S motif, it brought to the dramatic selectivity change of CO2 reduction production: dramatic decrease in HCOO− selectivity and increase in methanol selectivity. At −0.9 V vs RHE, maximum methanol faradaic efficiency (FE) and the selectivity of methanol arrived at 78.6% and 78.8%(Total-C FE was 95.5%), respectively. Some effective experiments involving of ECSA and charge transfer efficiency (Φ) certified that BS@Cx catalysts in the form of Bi-S motif exhibited higher intrinsic activity and selectivity, and overcame the energy barrier for methanol production. Coupled with PDOS of catalyst absorbed intermediates (OCHO* and CO*) and discussion of intermediates (COOH* and CH2O*), we bring forward a new possible pathway for catalyzing CO2 to methanol over BS@800. Further though microkinetic analysis with experimental Tafel slopes, we provided first-order understanding on the proposed reaction mechanisms, such as the rate-determining steps (RDS) and surface coverage (θ) of major reaction intermediates, and shed light on how rate-limiting steps can give rise to different Tafel slopes. This work may occur worthy insights into crystal structure engineering to achieve efficient electrocatalysts for selective CO2 conversion toward generation of valuable carbon-based chemicals.