Coordination Chemistry Engineered Polymeric Carbon Nitride Photoanode with Ultralow Onset Potential for Water Splitting.

Construction of an intimate film/substrate interface is of great importance for a photoelectrode to achieve efficient photoelectrochemical performance. Inspired by coordination chemistry, a polymeric carbon nitride (PCN) film is intimately grown on a Ti-coated substrate by an in situ thermal condensation process. The as-prepared PCN photoanode exhibits a record low onset potential (Eonset ) of -0.38 V versus the reversible hydrogen electrode (RHE) and a decent photocurrent density of 242 µA cm-2 at 1.23 VRHE for water splitting. Detailed characterization confirms that the origin of the ultralow onset potential is mainly attributed to the substantially reduced interfacial resistance between the Ti-coated substrate and the PCN film benefitting from the constructed interfacial sp2 N→Ti coordination bonds. For the first time, the ultralow onset potential enables the PCN photoanode to drive water splitting without external bias with a stable photocurrent density of ≈9 µA cm-2 up to 1 hour.

Designing efficient Bi2Fe4O9 photoanodes via bulk and surface defect engineering.

The Bi2Fe4O9 photoanode material is modified through a combined bulk and surface defect engineering (BSDE) strategy, delivering the highest photoresponse for Bi2Fe4O9 based materials. This work shows the advantage of BSDE in achieving efficient solar water splitting.

Reddish GaN:ZnO photoelectrode for improved photoelectrochemical solar water splitting.

Efficient light harvesting is one of the key prerequisites in improving the solar conversion efficiency for photoelectrochemical water splitting. As classic semiconductors for water splitting, the solid state solution GaN:ZnO based photoanodes exhibit poor water splitting efficiency mainly limited by its light absorption. To overcome this bottleneck, here we report that phosphorus modification shifts the absorption edge of GaN:ZnO from 480 nm to the red end of 650 nm and also leads to one order of magnitude increase of the carrier concentration. Further, taking the surface phosphate groups as anchors, cobalt can be adsorbed, leading to the in situ formation of cobalt phosphate as a cocatalyst for water oxidation, which results in drastically improved photocurrent density and stability. This work highlights the significance of phosphorization treatment in extending the light harvest and changing the surface reaction kinetics for an efficient solar conversion process.

Identifying Copper Vacancies and Their Role in the CuO Based Photocathode for Water Splitting.

Metal oxides are an important family of semiconductors for effective photoelectrodes in solar-to-chemical energy conversion. Defect engineering, such as modification of oxygen vacancy density, has been extensively applied in tailoring the optoelectric properties of photoelectrodes. Very limited attention has been paid to the influence of metal vacancies. Herein, we study metal vacancies in a typical CuO photocathode for photoelectrochemical (PEC) water splitting. The Cu vacancies can improve the charge carrier concentration, and facilitate the charge separation and transfer in the CuO photocathode. By changing the O2 partial pressure, the density of Cu vacancies can be tuned, which leads to improved PEC performance. The CuO photocathode prepared in pure O2 exhibits a 100 % photocurrent increase compared to that prepared in air. The promotion effect of Cu vacancies on the PEC is also observed in other Cu based photocathodes, showing the generic role of metal vacancies in efficient photocathodes.

Understanding the Roles of Oxygen Vacancies in Hematite-Based Photoelectrochemical Processes.

Oxygen vacancy (VO ) engineering is an effective method to tune the photoelectrochemical (PEC) performance, but the influence of VO on photoelectrodes is not well understood. Using hematite as a prototype, we herein report that VO functions in a more complicated way in PEC process than previously reported. Through a comprehensive analysis of the key charge transfer and surface reaction steps in PEC processes on a hematite photoanode, we clarify that VO can facilitate surface electrocatalytic processes while leading to severe interfacial recombination at the semiconductor/electrolyte (S-E) interface, in addition to the well-reported improvements in bulk conductivity. The improved bulk conductivity and surface catalysis are beneficial for bulk charge transfer and surface charge consumption while interfacial charge transfer deteriorates because of recombination through VO -induced trap states at the S-E interface.