Fabrication of interface with capping-bonding synergy to boost CO2 electroreduction to formate

The production of formic acid/formate from electrochemical CO 2 reduction reaction (CO 2 RR) is fascinating but challenging due to the lack of highly active electrocatalysts. Herein, uniform PVP-capped bismuth nanospheres (PVP@Bi-NSs) with a capping-bonding synergy were optimally fabricated to enhance the CO 2 RR to formate. This study unveils the reaction process in Bi-based solution. It was found that the formation of PVP@Bi-NSs experienced five stages of Bi-O 8 (I), Bi-O 3 (II), Bi-O 4 (III), Bi-Bi 6 (IV), and PVP@Bi-NSs (V), corresponding to the nucleation in precursor solution, Bi(OH) 3 precipitate, decomposition to KBiO 2 , reduction to metallic Bi, and PVP coating, respectively. By solvothermal treatment and simply modulating the KOH concentration in the precursor, the hydrophilic ends of PVP molecules can be well bonded to the Bi nanoparticles (Bi-NPs) to form a PVP-capping layer. Compared with the Bi-NPs without PVP coating, this uniform PVP@Bi-NSs displays a higher activity with a maximal Faradaic efficiency (FE) of 92.5 % and part current density ( J formate ) of 158.2 mA cm −2 at −0.9 V vs. RHE in the flow cell as well as excellent stability, which is comparable to the state-of-the-art Bi-based catalysts. The maximum J formate can reach 280 mA cm −2 with an FE of 87.3 % at −1.2 V vs. RHE, meeting the needs of industrial current density. Further characterizations show that the capping effect of PVP contributed to the uniform distribution of nanosized PVP@Bi-NSs, increasing the electrochemical surface areas (ECSAs) and the numbers of CO 2 RR active sites. The bonding effect of PVP to Bi-NPs enhanced the hydrophobic property of PVP@Bi-NPs, boosting the CO 2 absorption and suppressing the hydrogen evolution reaction (HER). DFT calculations reveal that this fabricated structure facilitates the generation of *OCHO intermediate and benefits formate yield. This work provides a fascinating strategy for the design of Bi-based catalysts, enabling interface engineering toward high-efficiency CO 2 RR.