Fengqiang Xiong

Visible light driven overall water splitting using cocatalyst/BiVO4 photoanode with minimized bias†

BiVO4 and many other semiconductor materials are ideal visible light responsive semiconductors, but are insufficient for overall water splitting. Upon loading water oxidation cocatalyst, for example Co-borate (denoted as CoBi) used here, onto BiVO4 photoanode, it is found that not only the onset potential is negatively shifted but also the photocurrent and the stability are significantly improved. And more importantly, PEC overall water splitting to H2 and O2 is realized using CoBi/BiVO4 as photoanode with a rather low applied bias (less than 0.3 V vs. counter electrode) in a two-electrode scheme, while at least 0.6 V is needed for bare BiVO4. This work demonstrates the practical possibility of achieving overall water splitting using the PEC strategy under a bias as low as the theoretical minimum, which is the difference between the flat band and proton reduction potential for a photoanode thermodynamically insufficient for water reduction. As long as the water oxidation overpotential is overcome with an efficient cocatalyst, the applied bias of the whole system is only used for that thermodynamically required for the proton reduction.

Low-cost and high-performance CoMoS4 and NiMoS4 counter electrodes for dye-sensitized solar cells

Porous chalcogels CoMoS4 and NiMoS4 made by a facile solution reaction displayed good electrocatalytic activity in the redox reaction of the I(-)/I3(-) shuttle. Dye-sensitized solar cells with these ternary compounds as counter electrodes (CEs) showed photovoltaic performance similar to the devices made with noble metal platinum CE (7.46%).

Enabling an integrated tantalum nitride photoanode to approach the theoretical photocurrent limit for solar water splitting

The feasibility of photoelectrochemical (PEC) water-splitting cells relies on the development of high-performance photoanodes. Significant progress has been made in the discovery of narrow bandgap semiconductors as promising photoanodes. However, the rational design of photoanode architecture that brings the potentials of narrow bandgap semiconductors into fruition for efficient PEC water oxidation still remains a key challenge. Herein, we show a highly efficient photoanode system consisting of a tantalum nitride (Ta3N5) semiconductor for light harvesting, hole-storage layers (Ni(OH)x/ferrhydrite) that mediate interfacial charge transfer from Ta3N5 to coupled molecular catalysts (Co cubane and Ir complex) for water oxidation and a TiOx blocking layer that reduces the surface electron–hole recombination. The integrated Ta3N5 photoanode exhibits a record photocurrent of 12.1 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode (RHE), which is nearly its theoretical photocurrent limit under sunlight (12.9 mA cm−2), suggesting that almost each pair of photogenerated charge carriers in Ta3N5 has been efficiently extracted and collected for solar water splitting.

Fabrication of multilayered TiO2 nanotube arrays and separable nanotube segments

Layered TiO2 nanotube arrays with new structures were prepared by switching the applied voltage of anodization of Ti. Taking advantage of the solvent effect, in an ethylene glycol electrolyte, arrays with thickness-modulated nanotube walls were prepared; in formamide electrolytes, nanotube arrays on 3-D nanopores, arrays with branched structures and arrays with separable nanotube segments were fabricated by designed voltage procedures.

Freestanding silicon films formed on ionic liquid surfaces

Freestanding silicon films with a thickness ranging from 1 nm to several micrometers were prepared by Cat-CVD onto ionic liquid ([BMIM][BF4]) surfaces for the first time. The films, obtained without a solid substrate, can be facilely characterized by TEM and AFM to study the film formation and growth process.

Enhanced photocatalytic water oxidation on ZnO photoanodes in a borate buffer electrolyte

Water oxidation performance of ZnO photoanodes was improved with a negative shift of ∼0.2 V in potential by a simple in situ photoelectrochemical reaction in borate buffer solution (BBS) or immersion at 75 °C in concentrated BBS. Electrochemical study of FTO electrodes shows an overpotential reduction effect of BBS treatment.