Decoupling Inherent Corrosion from Water Oxidation by Coating Bilayer Ionomers on Photoanodes

The local pH drop caused by water oxidation inevitably leads to photoanode corrosion and deactivation. As a well-studied photoanode, the stability of BiVO₄ restricts its application, despite the state-of-the-art efficiency approaching the theoretical limit. Herein, we demonstrate a facile strategy to improve the stability by sequentially coating bilayer ionomers of the anion exchange ionomer and proton exchange ionomer on a classic photoanode, NiFe/BiVO₄. This strategy creates a buffer layer that regulates the local pH near the photoanode surface. By modulating water dissociation and subsequent transfer of protons and hydroxyls, bilayer ionomers decouple the reaction-associated local pH changes from water oxidation, mitigating the inherently acidic corrosion toward photoanodes. An extended stability of 200 h is obtained, compared to less than 10 h without ionomer modification. This work provides a general strategy for stabilizing acid-sensitive photoanodes and offers insights in fabricating long-term stable systems related to photocatalysis and electrocatalysis.