Assessing and Quantifying Thermodynamically Concomitant Degradation during Oxygen Evolution from Water on SrTiO3

Theoxygen evolution reaction (OER) from water, while more stableon transition metal oxide surfaces than others, has nonetheless provedto be concomitant with charge-induced surface degradation. Since heterogeneousand nanostructured electrodes are often used and with a large excitationarea, the degradation can be difficult to quantify. Here, we utilizesingle crystalline SrTiO3, highly efficient photoexcitationof the OER, and a focused laser to spatially define the degradation.A repetitive, ultrafast laser pulse above the band gap energy is employed,which allows for highly varied exposure of the surface using differentscan methods. It also connects the work to the OER and its time-resolvedmechanisms. By characterizing the degradation using optical spectroscopyand electron microscopy, the material dissolution constitutes an upperbound of 6% of the charge passed in a pH 13 electrolyte, while forpH 7, it reaches 23%; the pH dependence is anticorrelated with theultrafast population of trapped charge. Although a minority component,the remarkable consistency of the 6% upper bound in the pH 13 electrolyteacross a large range of linearly increasing degradation volumes andchanging electrode composition defines a dominant lattice dissolutionreaction as thermodynamically concomitant with the OER. Along withthe pH dependence, the elemental composition of the degraded layerquantified by energy-dispersive and photoelectron and absorption X-rayspectroscopy suggests the relevance of certain chemical cation redepositionreactions. Altogether, using spatially and temporally defined photoexcitationof a crystalline surface provides a means to quantify semiconductingtransition metal oxide degradation during the OER and constricts itsmechanisms.

Automated summary

This study utilizes single crystalline SrTiO3, highly efficient photoexcitation of the OER, and a focused laser to spatially define the degradation. By characterizing the degradation using optical spectroscopy and electron microscopy, it is found that in a pH 13 electrolyte, the material dissolution constitutes an upper bound of 6% of the charge passed, while for pH 7, it reaches 23%.