Mesoporous In2O3 nanoflowers with oxygen vacancies for both alkaline and acidic CO2 electroreduction to formate/formic acid

The CO2 reduction reaction (CO2RR) is desirable, yet catalysts that exhibit high activity across different pH levels are lacking. Herein, mesoporous In2O3 nanoflowers (In2O3 NFs) with abundant oxygen vacancies (OV) are prepared by calcining an In2S3 precursor, which can selectively reduce CO2 to formate/formic acid. The In2O3 NFs deliver 88.4% formate faradaic efficiency (FE) at 500 mA cm−2 in a flow cell under alkaline conditions (pH = 13.5). Impressively, a high formic acid FE of ∼90% from 100 to 600 mA cm−2 is achieved in an acidic solution (pH = 2), representing one of the most promising acidic CO2RR performances to date. The confinement effect of the porous structure could enrich K+ ions to enhance the local alkaline microenvironment at the electrode interface during acidic CO2RR, which is the key to inhibiting the hydrogen evolution reaction (HER) and protecting the catalyst against acid corrosion. This work provides an efficient electrocatalyst for CO2RR in both alkaline and acidic electrolytes.