No abstract

The extensive deployment of the electrocatalytic CO 2 reduction reaction (CO 2 RR) is presently limited by the utilization of alkaline/neutral electrolytes in which carbonate formation severely reduces the carbon efficiency and electrolysis stability. By contrast, the CO 2 RR in a strong acid electrolyte can overcome these shortcomings, yet the hydrogen evolution reaction (HER) greatly outcompetes the CO 2 RR in acidic media. Herein, CO 2 reduction to HCOOH, a significant chemical intermediate in many industrial processes, was realized in strong acid (pH ≤ 1) through introducing K + cations into the electrolyte. The K + -assisted acidic CO 2 RR accordingly manufactured HCOOH with a high Faradaic efficiency of 92.2% @−1.23 V RHE and a commercially relevant current density of −237.1 mA cm −2 . More importantly, a high single-pass carbon efficiency of 27.4% for HCOOH production was demonstrated in acid, which exceeded the value obtained in the alkaline CO 2 RR. Further mechanistic studies demonstrated that K + can engineer the local microenvironment over the Bi catalyst surface by reducing the proton coverage to suppress the competing HER and creating local interaction to stabilize the *OCOH intermediate, which ultimately promotes high-efficiency CO 2 conversion to HCOOH in strong acidic media.

Electrochemical CO2 reduction to multicarbon products faces challenges of unsatisfactory selectivity, productivity, and long-term stability. Herein, we demonstrate CO2 electroreduction in strongly acidic electrolyte (pH ≤ 1) on electrochemically reduced porous Cu nanosheets by combining the confinement effect and cation effect to synergistically modulate the local microenvironment. A Faradaic efficiency of 83.7 ± 1.4% and partial current density of 0.56 ± 0.02 A cm−2, single-pass carbon efficiency of 54.4%, and stable electrolysis of 30 h in a flow cell are demonstrated for multicarbon products in a strongly acidic aqueous electrolyte consisting of sulfuric acid and KCl with pH ≤ 1. Mechanistically, the accumulated species (e.g., K+ and OH−) on the Helmholtz plane account for the selectivity and activity toward multicarbon products by kinetically reducing the proton coverage and thermodynamically favoring the CO2 conversion. We find that the K+ cations facilitate C-C coupling through local interaction between K+ and the key intermediate *OCCO.

Electrochemical structural reconstruction of catalysts may generate real active sites that differ from the initial catalyst, but is often ignored. Herein, combining in situ and ex situ techniques, it is identified that the bismuth nanosheets (NS) dotted with large numbers of coordinatively unsaturated pit sites is produced via the in situ structural reconstruction of Bi(OH)3 NS. Such reconstructed Bi NS shows greatly improved catalytic activity toward CO2 electroreduction, with a 2.6‐fold increase in current density compared with intact Bi NS, high Faradaic efficiency for HCOO− production (>95%), and an extraordinary turnover frequency of 0.35 s−1 at −0.98 VRHE. In addition, it delivers industrial‐relevant current density of 325 mA cm−2 without compromising selectivity in a flow cell. The mechanistic studies demonstrate that these coordinatively unsaturated sites acting as the real active sites favor the stabilization of key intermediate *OCHO, which thus facilitate the reaction kinetics for HCOO− production. This work not only provides a unique perspective on the construction of efficient catalysts for CO2 electroreduction, but also implies the importance in recognition of structural reconstruction.

The lack of highly efficient catalysts severely hinders large‐scale application of electrochemical hydrogen evolution reaction (HER) for hydrogen production from water. Herein, synergistic cascade hydrogen evolution boosting by combining the strategies of carbon layer confinement and surface oxophilicity modification is realized. The carbon layers confined ultrafine RuCr nanoparticles (RuCr@C) exhibit outstanding HER activity (j10 = 19 mV, turnover frequency = 4.25 H2 s‐1), surpassing the benchmark Pt/C and most of the reported HER catalysts. Combined experimental verifications and theoretical simulations reveal that surface adsorption modification and electronic structure regulation synergistically boosts the HER kinetics over the RuCr@C catalyst. The Volmer step is accelerated by stabilizing the final state of water dissociation (*H and *OH) through Cr doping, and the Heyrovsky step is promoted via carbon layers confinement. As such, this work highlights a synergistic cascade strategy to boost HER kinetics which is of fundamental importance to accelerate future advances in electrocatalysis.