(Invited) Electronic Tuning of Photo-Electro-Catalytic Processes By Intermediate-Band Oxides

Abstract

Intermediate-band oxides possess tunable transport energy levels: they can serve as chemically-stable, transparent conductive protective layers for durable photo- and electro-catalytic processes. They have initially shown to promote charge separation, practically interfacing the otherwise unstable light absorbers and protecting them against corrosion. The initial re-discovery of “leaky” TiO2 coatings utilize their Ti3+- defect bands to stabilize an entire class of Si, GaP, GaAs, CdTe, BiVO4 semiconductors, as well as structured Si pillars and GaAs wires for 1000s-hour operation under sunlight. Recently, a ternary protective coating of manganese-alloyed titanium oxide, (Ti,Mn)Ox, had achieved the incorporation of transition metal cation impurities, e.g. Mn3+, into an otherwise insulating TiO2 coating. Here, Mn compositions can reach as high as 70% for a 150°C growth, which cannot be achieved by any method other than ALD. The individual redox of the Mn3+ composes a continuous Mn-impurity band. On the one hand, this intermediate band induced electronic interactions between ALD coatings and underlying electro-catalysts, for boosting the hydrogen evolution activity of such buried interfaces. On the other hand, these oxide coatings have further shown to confine charge transport to specific electrochemical potentials and confine charge transfer to specific surface-attached intermediates, thus promoting product selectivity. To summarize, the tunable electronic structures of intermediate-band oxides enabled new strategies for controlling charge separation and charge transfer at liquid interfaces.