The interactions of CO2 with indium metal electrodes have been characterized for electrochemical formate production. The electrode oxidation state, morphology, and voltammetric behaviors were systematically probed. It was found that an anodized indium electrode stabilized formate production over time compared to etched indium electrodes and indium electrodes bearing a native oxide in applied potential range of -1.4 to -1.8 V vs SCE. In addition, it was observed that formate is the major product at unprecedentedly low overpotentials at the anodized surface. A surface hydroxide species was observed suggesting a mechanism of formate production that involves insertion of CO2 at the indium interface to form an electroactive surface bicarbonate species.

Polycrystalline CuRhO2 is investigated as a photocathode for the splitting of water under visible irradiation. The band edge positions of this material straddle the water oxidation and reduction redox potentials. Thus, photogenerated conduction band electrons are sufficiently energetic to reduce water, while the associated valence band holes are energetically able to oxidize water to O2. Under visible illumination, H2 production is observed with ~0.2 V underpotential in an air-saturated solution. In contrast, H2 production in an Ar-saturated solution was found to be unstable. This instability is associated with the reduction of the semiconductor forming Cu(s). However, in the presence of air or O2, bulk Cu(s) was not detected, implying that CuRhO2 is self-healing when air is present. This property allows for the stable formation of H2 with ca. 80% Faradaic efficiency.

Mg-doped CuFeO 2 delafossite is reported to be photoelectrochemically active for CO 2 reduction. The material was prepared via conventional solid-state methods, and subsequently assembled into an electrode as a pressed pellet. Addition of a Mg 2+ dopant is found to substantially improve the conductivity of the material, with 0.05% Mg-doped CuFeO 2 electrodes displaying photocathodic currents under visible irradiation. Photocurrent is found to onset at irradiation wavelengths of ∼800 nm with the incident photon-to-current efficiency reaching a value of 14% at 340 nm using an applied electrode potential of −0.4 V vs SCE. Photoelectrodes were determined to have a −1.1 V vs SCE conduction band edge and were found capable of the reduction of CO 2 to formate at 400 mV of underpotential. The conversion efficiency is maximized at −0.9 V vs SCE, with H 2 production contributing as a considerable side reaction. These results highlight the potential to produce Mg-doped p-type metal oxide photocathodes with a band structure tuned to optimize CO 2 reduction.

The chemistry of the electrocatalytic reduction of CO 2 using nitrogen containing heteroaromatics is further explored by the direct comparison of imidazole and pyridine catalyzed CO 2 reduction at illuminated iron pyrite electrodes. The mechanism of imidazole based catalysis of CO 2 reduction is investigated by analyzing the catalytic activity of a series of imidazole derivatives using cyclic voltammetry. While similar product distributions are obtained for both imidazole and pyridine, the imidazole catalyzed reduction of CO 2 likely proceeds via a very different mechanism involving the C2 carbon of the imidazole ring.

Metallic Indium and its oxides are useful in electronics applications in transparent conducting electrodes, as well as in electrocatalytic applications. In order to understand more fully the speciation of the indium and oxygen composition of the indium surface exposed to atmospheric oxidants, XPS, HREELS, and TPD were used to study the indium surface exposed to water, oxygen, and carbon dioxide. Clean In and authentic samples of In 2 O 3 and In(OH) 3 were examined with XPS to provide standard spectra. Indium was exposed to O 2 and H 2 O, and the ratio of O 2to OHin the O1s XPS region was used to monitor oxidation and speciation of the surface. HREELS and TPD indicate that water dissociates on the indium surface even at low temperature, and that In 2 O 3 forms at higher temperatures. Initially, OH-is the major species at the surface. Pure In 2 O 3 is also OH-terminated following water exposure. Ambient pressure XPS studies of water exposure to these surfaces suggest that high water pressures tend to passivate the surface, inhibiting extensive oxide formation. † These authors contributed equally to the work described here.