Au-Cu bimetallic thin films with controlled composition were fabricated by magnetron sputtering co-deposition, and their performance for the electrocatalytic reduction of CO ₂ was investigated. The uniform planar morphology served as a platform to evaluate the electronic effect isolated from morphological effects while minimizing geometric contributions. The catalytic selectivity and activity of Au-Cu alloys was found to be correlated with the variation of electronic structure that was varied with tunable composition. Notably, the d-band center gradually shifted away from the Fermi level with increasing Au atomic ratio, leading to a weakened binding energy ofCO, which is consistent with low CO coverage observed in CO stripping experiments. The decrease in theCO binding strength results in the enhanced catalytic activity for CO formation with the increase in Au content. In addition, it was observed that copper oxide/hydroxide species are less stable on Au-Cu surfaces compared to those on the pure Cu surface, where the surface oxophilicity could be critical to tuning the binding strength ofOCHO. These results imply that the altered electronic structure could explain the decreased formation of HCOO ^- on the Au-Cu alloys. In general, the formation of CO and HCOO ^- as main CO ₂ reduction products on planar Au-Cu alloys followed the shift of the d-band center, which indicates that the electronic effect is the major governing factor for the electrocatalytic activity of CO ₂ reduction on Au-Cu bimetallic thin films.

Amorphous silicon carbide (a-SiC:H) is a promising material for photoelectrochemical water splitting owing to its relatively small band-gap energy and high chemical and optoelectrical stability. This work studies the interplay between charge-carrier separation and collection, and their injection into the electrolyte, when modifying the semiconductor/electrolyte interface. By introducing an n-doped nanocrystaline silicon oxide layer into a p-doped/intrinsic a-SiC:H photocathode, the photovoltage and photocurrent of the device can be significantly improved, reaching values higher than 0.8V. This results from enhancing the internal electric field of the photocathode, reducing the Shockley-Read-Hall recombination at the crucial interfaces because of better charge-carrier separation. In addition, the charge-carrier injection into the electrolyte is enhanced by introducing a TiO₂ protective layer owing to better band alignment at the interface. Finally, the photocurrent was further enhanced by tuning the absorber layer thickness, arriving at a thickness of 150nm, after which the current saturates to 10mAcm^-2 at 0V vs. the reversible hydrogen electrode in a 0.2m aqueous potassium hydrogen phthalate (KPH) electrolyte at pH4.

Bismuth vanadate (BiVO₄) is one of the most efficient light absorbing metal oxides for solar water splitting. BiVO₄ photoanodes immersed in an electrolyte in an open circuit configuration and exposed to simulated solar illumination for prolonged time achieve superior photoelectrochemical (PEC) activity. This photocharging (PC) effect is capable of almost completely overcoming the surface and bulk limitations of BiVO₄. Herein we show that alkaline conditions favor the PC effect; specifically BiVO₄ photoanodes subjected to PC treatment at pH 10 achieve a record high photocurrent for undoped and uncatalyzed BiVO₄ of 4.3 mA cm^-2 @ 1.23 V_RHE, an outstandingly low onset potential of 0.25 V_RHE, and a very steep photocurrent onset. Alkaline conditions also facilitate excellent external and internal quantum efficiencies of 75 and 95% respectively (average in the 440 nm > λ > 330 nm range). Moreover, impedance spectroscopy and in situ XAS study suggest that electronic, structural and chemical properties of the bulk of these films remain unchanged during the PC treatment. However, appreciable changes in the surface-related properties take place. Ultimately, our results indicate that the improved activity of PC-BiVO₄ is enhanced by surface reaction pathways of the semiconductor-liquid junction, which is directly correlated with the electrochemical environment in which it is modified.