Photoelectrochemical cells promise sustainable production of hydrogen fuel from water using sunlight. Currently, the most efficient photocathodes are based on III-V phosphides; however, photocorrosion in the electrolyte solution remains a significant challenge. In an effort to better understand the complex chemistry active at the electrode-electrolyte interface of III-V semiconductor photocathodes, we have performed extensive first-principles molecular dynamics simulations on GaP/InP(001). In addition to explicitly accounting for the presence of liquid water, we have also studied the effect of experimentally reported oxygen-derived surface adsorbates.We find that surface oxygen dramatically alters the nature of the electrode-electrolyte interface, providing a kinetically feasible pathway for water dissociation. This results in the formation of an interfacial hydrogen-bond network. Interestingly, the dynamics of this network are qualitatively different for GaP and InP, with the latter exhibiting much greater network fluidity. We suggest that this translates to the capability of InP for long-range hydrogen transport in a way kinetically inaccessible to GaP. Implications for understanding initial interface formation, as well as the kinetics of photoelectrochemical H2 evolution and photocorrosion processes on GaP and InP surfaces, will be discussed in detail.This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

Interfacial chemistry of III-V semiconductors for photoelectrochemical water splitting

246th National Meeting (2013)

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