Immobilized Azole Layer Tunes Interfacial Hydrogen Source for CO<sub>2</sub> Electroreduction in Strong Acid
Yaohui Shi, Yu Yang, Aoni Xu, Kwun Nam Hui, Fengwang Li, Jie Zeng
Abstract
Achieving selective electrochemical CO 2 reduction reaction (CO 2 RR) in strong acid holds potential to resolve the “carbonate formation” problem yet is hindered by the competing hydrogen evolution reaction (HER). The interplay between different hydrogen sources (i.e., H + vs H 2 O) and its impact on CO 2 RR selectivity in acidic electrolytes remains poorly understood. Herein, we introduce an immobilized N-containing azole layer (phTA) onto Bi catalysts to dynamically regulate the interfacial hydrogen source in strong acid (pH 0.4). Combining experimental and modeling approaches, we reveal a dual mechanism dependent on local interfacial conditions. At lower potentials with high local [H + ], the protonated phTA layer (NH + sites) serves as a proton relay while electrostatically shielding bulk H + diffusion. Conversely, at higher potentials with low local [H + ], less protonated phTA disrupts the interfacial hydrogen-bond network, impeding Grotthuss-type proton transport, thus suppressing HER through hydrogen source shifts toward H 2 O. As a result, the faradaic efficiency for formic acid (FE HCOOH ) on Bi-phTA significantly increases to 36% at −300 mA cm –2 (pH 0.4) compared to <10% for bare Bi. This work demonstrates the controlled manipulation of the hydrogen source via a dynamically responsive organic layer, highlighting the importance of managing interfacial hydrogen species for enhancing the CO 2 RR in acid.