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.     

Intercalated Iridium Diselenide Electrocatalysts for Efficient pH‐Universal Water Splitting

Developing bifunctional catalysts for both hydrogen and oxygen evolution reactions is a promising approach to the practical implementation of electrocatalytic water splitting. However, most of the reported bifunctional catalysts are only applicable to alkaline electrolyzer, although a few are effective in acidic or neutral media that appeals more to industrial applications. Here, a lithium‐intercalated iridium diselenide (Li‐IrSe₂) is developed that outperformed other reported catalysts toward overall water splitting in both acidic and neutral environments. Li intercalation activated the inert pristine IrSe₂ via bringing high porosities and abundant Se vacancies for efficient hydrogen and oxygen evolution reactions. When Li‐IrSe₂ was assembled into two‐electrode electrolyzers for overall water splitting, the cell voltages at 10 mA cm^?2 were 1.44 and 1.50 V under pH 0 and 7, respectively, being record‐low values in both conditions.     

Negative Charging of Transition‐Metal Phosphides via Strong Electronic Coupling for Destabilization of Alkaline Water

Heterogeneous electrocatalysis typically involves charge transfer between surface active sites and adsorbed species. Therefore, modulating the surface charge state of an electrocatalyst can be used to enhance performance. A series of negatively charged transition‐metal (Fe, Co, Ni, Cu,and NiCo) phosphides were fabricated by designing strong electronic coupling with hydr(oxy)oxides formed in situ. Physicochemical characterizations, together with DFT computations, demonstrate that strong electronic coupling renders transition‐metal phosphides negatively charged. This facilitates destabilization of alkaline water adsorption and dissociation to result in significantly improved H₂ evolution. Negatively charged Ni₂P/nickel hydr(oxy)oxide for example exhibits a significantly low overpotential of 138 mV at 100 mA cm^?2, superior to that without strong electronic coupling and also commercial Pt/C.     

A Rapid Microwave‐Assisted Thermolysis Route to Highly Crystalline Carbon Nitrides for Efficient Hydrogen Generation

Highly crystalline graphitic carbon nitride (g‐C₃N₄) with decreased structural imperfections benefits from the suppression of electron–hole recombination, which enhances its hydrogen generation activity. However, producing such g‐C₃N₄ materials by conventional heating in an electric furnace has proven challenging. Herein, we report on the synthesis of high‐quality g‐C₃N₄ with reduced structural defects by judiciously combining the implementation of melamine–cyanuric acid (MCA) supramolecular aggregates and microwave‐assisted thermolysis. The g‐C₃N₄ material produced after optimizing the microwave reaction time can effectively generate H₂ under visible‐light irradiation. The highest H₂ evolution rate achieved was 40.5 μmol h⁻¹, which is two times higher than that of a g‐C₃N₄ sample prepared by thermal polycondensation of the same supramolecular aggregates in an electric furnace. The microwave‐assisted thermolysis strategy is simple, rapid, and robust, thereby providing a promising route for the synthesis of high‐efficiency g‐C₃N₄ photocatalysts.