High-efficiency photoelectrochemical water-splitting devices require integrating electrocatalysts (ECs) onto light-absorbing semiconductors (SCs), but the energetics and charge transfer processes at SC|EC interfaces are poorly understood. In order to understand ECs on photoanodes, we fabricate model EC-coated single-crystal TiO2 electrodes and directly probe SC|EC interfaces in situ using a new dual-electrode photoelectrochemistry technique to independently monitor and control the potential/current at both the SC and the EC.1 We discover that redox-active ion-permeable ECs such as Ni(OH)2/NiOOH yield �adaptive� SC|EC junctions where the effective Schottky barrier height changes in situ with the oxidation level of the EC. In contrast, dense, ion-impermeable IrOx ECs yield constant-barrier-height �buried� junctions. Conversion of dense, thermally deposited NiOx on TiO2 into ion-permeable Ni(OH)2/NiOOH correlated with increased apparent photovoltage and fill-factor. A new theory of adaptive  EC|SC junctions is proposed and applied via numerical simulation to understand this behavior.2  The theory can also be used to understand catalyst-modified hydrogen-evolving photocathodes as well as catalyst-modified visible-light-absorbing oxides such as BiVO4, and experiments are underway to directly test the predictions. These results provide new insight into the dynamic behavior of SC|EC interfaces that help guide the design of efficient SC|EC devices. They also illustrate a new class of adaptive semiconductor junctions.  (1)       Lin, F.; Boettcher, S. W. Adaptive semiconductor-electrocatalyst junctions in water splitting photoanodes. Nature. Mater. 2014 , 13, 81-86.(2)       Mills, T. J.; Boettcher, S. W. Theory and simulations of electrocatalyst-coated semiconductor electrodes for solar water splitting. Submitted. 2013 .

Semiconductor-electrocatalyst contacts: Theory, experiment, and applications to solar water photoelectrolysis

248th National Meeting (2014)

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