Discretized Photoanodes Design Tolerates Nanoscale Corrosion Defects for >600 Hours Stable Photoelectrochemical Water Oxidation

For photoelectrode used for solar fuel generation, one key characteristic is photoelectrode stability. They are efficient and have tunable bandgaps that could in principle allow in tandem structures for unassisted, high-efficiency water splitting and other applications. However, III-V based photoelectrodes are also reported to suffer continuous photo corrosion in aqueous solution. Even with the coating protection, catastrophic failure will still occur due to pitting corrosion at defect sites in protection layers, which limited the device stability to be less than 100 hours. In our recent work (doi:10.1021/acsenergylett.0c02521), we compare and discuss about the corrosion mechanism for continuous and discrete electrode, and then propose a new stabilization strategy by confining the nanoscale pinhole from propagating. Firstly, we recognize that the long-term failure mode of planar III-V materials involves pitting corrosion due to extrinsic defects in amorphous TiO2 protective layers. Then, we show that extended stability can be obtained in structures that isolated defects electrically and thus prevented deleterious corrosion from spreading laterally, undercutting the protection layers and active layers, and leading to catastrophic failure of the photoanode. When grown on insulating or self-passivating substrates, these nanowire arrays indeed exhibited extended stability and operated stably for over 600 hours of photoanodic water oxidation, as compared to the control experiments that yielded much less stability due to a lack of defect-tolerance in the device structure. This work employs comprehensive characterizations including multiscale SEM/EDS, TEM, and electrochemical methods to the electrodes before and after the stability test. We believe this discovery and study should help advance the understanding of corrosion mechanism for coated photoelectrode and the mitigation strategy.