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A case study of the complex interplay of electrodes surface potentials and reactants oxidation potentials for photofuel cell (PFC) operation is highlighted. Cyclic voltammetry (CV) reveals that InN/InGaN quantum dots (QDs) are active for H2O2 and water oxidation in the light. InGaN nanowires (NWs) are active for H2O2 oxidation in the light and dark. In H2O2 PFC operation, high performance is achieved for InN/InGaN QDs in the light. NWs operate with lower performance in the light and dark. Similarly, with glucose as biofuel, the NWs are active in the light and dark, the QDs only in the light. All results are explained by the surface states on the c-plane QDs and m-plane NW sidewalls, the oxidation potentials of H2O2, water and glucose, and the catalytic activity of the QDs.

We present a basic, comprehensive study of the electrocatalytic activity of epitaxial InN/InGaN quantum dots (QDs) by cyclic voltammetry, electrochemical impedance spectroscopy, linear sweep voltammetry and capacitance-voltage measurements, using the ferro/ferricyanide redox probe. Key is the direct proof of the dependence of the catalytic activity on the QD structural properties and of the existence and overall tunability of high positive surface charge on the QDs being in origin of the catalytic activity together with the zero-dimensional electronic properties. This fundamental assessment paves the way to fine-tuning the artificial QD structure as efficient catalyst to further boost the performance of biosensors and photoanodes for solar hydrogen generation. Keywords: Quantum dots, InN, InGaN, Catalysis