Observing Long-lived Photogenerated Holes in Cobalt Oxyhydroxide Oxygen Evolution Catalysts

Steady-state and time-resolved spectroelectrochemical optical absorption techniques were used to investigate photoexcited states of amorphous cobalt-phosphate oxyhydroxide (CoPi) and cobalt-borate oxyhydroxide (CoBi) oxygen evolution catalysts. These materials revealed concurrent spectroelectrochemical intensity changes in their ground state and photoexcited visible spectra, providing insights into the dynamics of defect states attributable to trapped holes. Notably, long-lived photoexcited states, assignable to hole-based defects persisting beyond 10 ms in H2O, were observed in CoPi and CoBi for the first time. Both thin films exhibited distinct dynamics, however, highlighting differences in their structural and electronic properties despite strong similarities in absorption spectral profiles. These results provide further insight into the differences between the electronic properties and dynamics of CoPi and CoBi, which have been challenging to structurally and electronically characterize due to their amorphous nature.