Metal-free boron nanosheet as “buffer electron pool” for urea and ethanol synthesis via C–N and C–C coupling

Abstract

The electrocatalytic synthesis of high value-added urea and ethanol from carbon dioxide (CO₂) and nitric oxide (NO) via C–N and C–C coupling reactions is one of the most attractive approaches. Nevertheless, the development of a bi-functional metal-free electrocatalyst with long-term stability, activity, selectivity, and low cost remains a great challenge to date. Herein, based on the concept of “buffer electron pool”, a novel metal-free electrocatalyst, β₁₂ boron nanosheet materials (β₁₂-BM) with local electrophilic and nucleophilic regions is proposed by combining density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations for urea and ethanol production. The results reveal that β₁₂-BM has a superior intrinsic basal activity for urea formation with extremely low limiting potential of −0.09 V and −0.75 V for ethanol formation in the gas phase. Moreover, dynamic barriers were found to be 0.62 eV and 0.60 eV for the two steps of C–N coupling and 1.11 eV for C–C coupling by a “slow-growth” sampling approach in the explicit water molecules model. Importantly, β₁₂-BM can significantly suppress competitive reactions such as hydrogen evolution reaction (HER) and NO reduction reaction (NORR). The present work reports the bi-functional metal-free β₁₂-BM for urea and ethanol synthesis, offering a deep insight into the underlying chemistry of C–N and C–C coupling reactions that could guide the sustainable synthesis of other indispensable chemicals.