Electrochemically Dismantled Perovskite with Cooperative Catalysis for CO2-to-Formate Conversion

Abstract

Electrochemical reduction of carbon dioxide (CO2RR) driven by sustainable energy resources holds great promise for realizing the zero net emission of CO2 by converting them to value-added fuels.1–4 For the past few years, substantial efforts have been devoted to boosting CO2RR using different nanostructured catalysts. However, the complicated synthesis procedures and low product yields are usually associated with many of these catalysts, which hinder their scalability. More importantly, many catalysts suffer from the low catalytic activities, high overpotentials, and unsatisfactory selectivity, which collectively impede the large-scale applications of CO2RR technique. In this study, we pursue initiating the CO2 conversion on perovskite-based catalysts BaBiO3 (BBO) to selectively produce formate (FA). The structural/phase evolution of BBO under cathodic potentials, the catalytic performances of electrochemical and photoelectrochemical reduction of CO2RR, and the effect of non-active A-site element (Ba) will be investigated in detail.Herein, BBO perovskite is fabricated by annealing the sol-gel Ba2+/Bi3+ nitrate mixture at high temperatures. Extensive physical characterizations show that under negative potentials, BBO pre-catalysts undergo irreversible structural and phase transformations, giving rise to Bi metallene with atomic-scale thickness and enlarged surface area, as supported by X-ray diffraction analysis and transmission electron microscopy (Figure 1a, and 1b). Using the fully electrochemically reduced BBO, a near-unity selectivity towards formate (FA) can be achieved at the potential of – 1.2 V vs. RHE in 0.1M KHCO3 solution with the typical H-type electrochemical cell. By coupling the state-of-the-art BiVO3 photoanode to the BBO dark cathode, FA can be generated at a of 80.0 % at a cell voltage of 2.5 V in a PEC cell. Contrarily, only < 1.0 % can be detected at 2.5 V without solar irradiation. Meanwhile, inductively coupled plasma optical emission spectrometry (ICP-OES) analysis suggests that A-site elements (Ba2+) are simultaneously released from the BBO lattice and diffuse to the electrolyte as a result of the complete reduction of BBO. The effect of Ba2+ - containing electrolytes on the CO2RR product distributions have been studied, and the results show that Ba2+ can either facilitate or impede FA production depending on both the external potential and the concentration of Ba2+ (Figure 1c). Specifically, high Ba2+ concentration and more negative potentials (i.e., 25 mM Ba2+ and -1.1 - -1.3 V vs. RHE) tend to favor HER over CO2RR due to the formation of BaCO3 precipitates, whereas low Ba2+ concentrations and more positive potentials (i.e., 2.5 and 7.5 mM Ba2+ and -0.9 - -1.1 V vs. RHE) can significantly enhance the selectivity towards FA. Density functional theory (DFT) calculations show that suitable barium ion adsorption promotes CO2-to-FA conversion by regulating the adsorption strength of *OCHO and *HCOOH intermediates. Our study utilizes both A- and B- site elements in BBO to benefit CO2 conversion, which may be extended to other perovskite electrocatalysts for CO2RR.