Sponge-inspired catalyst design for durable acidic CO2 reduction at low K+ concentration

Acidic electrochemical CO2 reduction (CO2RR) typically requires K+ ions to create a local H+-depleted microenvironment, suppressing competing hydrogen evolution reaction (HER). Excessive localized K+ causes salt precipitation, compromising electrolysis stability. Achieving stable operation with high Faradaic efficiency (FE) at low K+ concentrations remains a crucial challenge for conventional nanomaterials. Inspired by water-trapping function of sponges, we design a three-dimensional interconnected porous cubic SnO2 electrocatalyst (SnO2 sponge) that confines OH– within porous channels to consume proton influx from the bulk, enabling durable acidic CO2RR towards formic acid (HCOOH). Theoretical and experimental studies reveal the SnO2 sponge sustains substantially higher OH– concentration than dispersed SnO2 nanoparticles. At pH 1.82, the SnO2 sponge achieves 94.5% FEHCOOH at 800 mA cm–2. With only 0.075 M K+, it retains 95.2% FEHCOOH at 400 mA cm–2. Notably, it enables continuous HCOOH production at 400 mA cm–2 with 97.7% FEHCOOH for over 390 h without cleaning. This work provides a promising strategy for durable and efficient CO2RR in acidic media with low K+ concentrations. Acidic CO2 reduction typically requires high K+ to suppress hydrogen evolution, which can cause salt precipitation and system instability. Here, the authors report a porous SnO2 sponge that traps OH− ions, enabling stable and highly efficient formic acid production at low K+ concentrations.