Boosting CO Production in Electrocatalytic CO₂ Reduction on Highly Porous Zn Catalysts

Abstract

Earth-abundant electrocatalysts are desirable for the efficient and selective reduction of CO2 to value-added chemicals. Here, a low-cost porous Zn electrocatalyst is synthesized using a facile electrodeposition method to boost the performance of CO2 electrocatalytic reaction (CO2RR). In an H-cell reactor, the porous Zn catalyst can convert CO2 to CO at a remarkably high faradaic efficiency (FE, ∼95%) and current density (27 mA cm–2) at −0.95 V versus the reversible hydrogen electrode. Detailed electrokinetic studies demonstrate that instead of the enhanced intrinsic activity, the dramatically increased active sites play a decisive role in improving the catalytic activity. In addition, the high local pH induced by the highly porous structure of Zn results in enhanced CO selectivity because of the suppressed H2 evolution. Furthermore, we present a straightforward strategy to transform the porous Zn electrode into a gas diffusion electrode. This way, the CO2RR current density can be boosted to 200 mA cm–2 with ∼84% FE for CO at −0.64 V in a flow-cell reactor, which is, to date, the best performance observed over non-noble CO2RR catalysts.

Heterogeneous Single‐Atom Catalysts for Electrochemical CO2 Reduction Reaction

“…Zinc is a CO‐producing metal for CO 2 RR. Various nanostructured Zn catalysts have been constructed to convert CO 2 to CO, such as porous Zn catalysts, [ 133,134 ] Zn nanoparticles, [ 135 ] Zn nanosheet, [ 136 ] and Zn dendrites. [ 137 ] Similar to its metal/oxide counterparts, single‐atom Zn catalysts have also been reported to convert CO 2 into CO through CO 2 RR.…”

Progress in development of electrocatalyst for CO2 conversion to selective CO production

“…Therefore, a maximum CO FE of 94.2% was achieved at –0.8 V RHE for 15 hours in the long‐term test, unlike for the bulk ZnS (Figure K). In the very recent past, highly porous P‐Zn catalysts fabricated by electrodeposition onto the Cu mesh was shown to enable CO FE to reach 94.4% with a high current density of 27 mA cm –2 at –0.95 V RHE and a CO production rate of 671 μmol h –1 cm –2 at –1.1 V RHE , which is superior in comparison to previous Zn‐based reports (Figure L) . The enlarged electrochemical surface area and the strengthened local pH effect in the porous structure are ascribed to the dramatically improved activity.…”

“…Meanwhile, recent dramatic progress of nanostructured Zn catalysts, even in the popular bicarbonate electrolyte, has been made based on an introduction of various secondary phases to Zn catalysts . The Zn 94 Cu 6 foam catalyst generated by introducing Cu achieved a CO FE of 90% at –0.95 V RHE .…”

“…This led to avoid the high pH conditions, which can cause the mass transport limitation of CO 2 and consequently decrease selectivity of CO 2 RR . Interestingly, however, it has been observed that increasing (local) pH rather helps favor CO 2 RR over HER due to peripherally decreasing H + concentration on the electrode . These results indicate that the impact of pH should also be considered from the kinetics standpoint of HER, which is the spontaneously competing reaction of CO 2 ‐to‐CO in the aqueous electrolyte.…”

“…62,70 Meanwhile, recent dramatic progress of nanostructured Zn catalysts, even in the popular bicarbonate electrolyte, has been made based on an introduction of various secondary phases to Zn catalysts. [67][68][69]71 The Zn 94 Cu 6 foam catalyst generated by introducing Cu achieved a CO FE of 90% at -0.95 V RHE . 71 Wang et al developed the Li electrochemical tuning method for synthesizing interconnected ultra-small Zn nanoparticles from ZnO with enriched grain boundaries, which could enhance CO FE up to 91% at -1.17 V RHE .…”