Mixed-metal nanosheet water oxidation catalysts made by pulsed-laser ablation in liquids - Part 2: Mechanistic insights gained by novel in-situ spectroscopies

Abstract

Sustainable energy solns. impact every aspect of human life. National security, health, access to clean water, the extent of climate change, and biodiversity all critically depend on the global availability of clean, affordable energy. The sun is our most abundant source of energy; more energy from sunlight strikes earth within a single hour than mankind consumes per yr. To sustainably power the planet, sunlight capture, charge transport, and catalysis are needed for fuel prodn. through water splitting. Water oxidn. provides reducing equiv. through a complex four-electron transfer process. Sufficiently active, robust, earth-abundant catalysts for this important reaction are much needed yet still elusive; they will only be discovered through rational catalyst design guided by mechanistic insights into individual reaction steps. We recently reported highly efficient [NiFe] - layered double hydroxide water oxidn. nanocatalysts [Hunter, Blakemore, Deimund, Gray, Winkler, Mueller, J. 2014, 136, 13118]. To gain mechanistic information, several in-situ electrochem. spectroscopies (i.e. IR, Raman, EPR, and x-ray absorption spectroscopies) have been developed, by which transient species during catalytic turnover were detected. We applied potentials to the catalyst nanosheets, at which in aq. electrolyte water oxidn. would occur, but instead we used non-aq. media to halt the catalytic cycle; strategic injection of water led to turnover, and short-lived species could be identified. This way, we obtained exptl. evidence for intermediates required for efficient water oxidn.