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

Acidic electrochemical CO 2 reduction (CO 2 RR) 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 SnO 2 electrocatalyst (SnO 2 sponge) that confines OH – within porous channels to consume proton influx from the bulk, enabling durable acidic CO 2 RR towards formic acid (HCOOH). Theoretical and experimental studies reveal the SnO 2 sponge sustains substantially higher OH – concentration than dispersed SnO 2 nanoparticles. At pH 1.82, the SnO 2 sponge achieves 94.5% FE HCOOH at 800 mA cm –2 . With only 0.075 M K + , it retains 95.2% FE HCOOH at 400 mA cm –2 . Notably, it enables continuous HCOOH production at 400 mA cm –2 with 97.7% FE HCOOH for over 390 h without cleaning. This work provides a promising strategy for durable and efficient CO 2 RR in acidic media with low K + concentrations.