Multilayer Strategy for Photoelectrochemical Hydrogen Generation: New Electrode Architecture that Alleviates Multiple Bottlenecks

Porous Microreactor Chip for Photocatalytic Seawater Splitting over 300 Hours at Atmospheric Pressure

Photocatalytic seawater splitting is an attractive way for producing green hydrogen. Significant progresses have been made recently in catalytic efficiencies, but the activity of catalysts can only maintain stable for about 10 h. Here, we develop a vacancy-engineered Ag3PO4/CdS porous microreactor chip photocatalyst, operating in seawater with a performance stability exceeding 300 h. This is achieved by the establishment of both catalytic selectivity for impurity ions and tailored interactions between vacancies and sulfur species. Efficient transport of carriers with strong redox ability is ensured by forming a heterojunction within a space charge region, where the visualization of potential distribution confirms the key design concept of our chip. Moreover, the separation of oxidation and reduction reactions in space inhibits the reverse recombination, making the chip capable of working at atmospheric pressure. Consequently, in the presence of Pt co-catalysts, a high solar-to-hydrogen efficiency of 0.81% can be achieved in the whole durability test. When using a fully solar-driven 256 cm2 hydrogen production prototype, a H2 evolution rate of 68.01 mmol h-1 m-2 can be achieved under outdoor insolation. Our findings provide a novel approach to achieve high selectivity, and demonstrate an efficient and scalable prototype suitable for practical solar H2 production.

Rapid Outgassing of Hydrophilic TiO2 Electrodes Achieves Long-Term Stability of Anion Exchange Membrane Water Electrolyzers

The state-of-the-art anion-exchange membrane water electrolyzers (AEMWEs) require highly stable electrodes for prolonged operation. The stability of the electrode is closely linked to the effective evacuation of H2 or O2 gas generated from electrode surface during the electrolysis. In this study, we prepared a super-hydrophilic electrode by depositing porous nickel-iron nanoparticles on annealed TiO2 nanotubes (NiFe/ATNT) for rapid outgassing of such nonpolar gases. The super-hydrophilic NiFe/ATNT electrode exhibited an overpotential of 235 mV at 10 mA cm-2 for oxygen evolution reaction in 1.0 M KOH solution, and was utilized as the anode in the AEMWE to achieve a current density of 1.67 A cm-2 at 1.80 V. In addition, the AEMWE with NiFe/ATNT electrode, which enables effective outgassing, showed record stability for 1500 h at 0.50 A cm-2 under harsh temperature conditions of 80 ± 3 °C.

Decade Milestone Advancement of Defect-Engineered g-C3N4 for Solar Catalytic Applications

Over the past decade, graphitic carbon nitride (g-C3N4) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C3N4 is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the "all-in-one" defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultra-active coordinated environment (M-Nx, M-C2N2, M-O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra (fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C3N4 "customization", motivating more profound thinking and flourishing research outputs on g-C3N4-based photocatalysis.

Enhanced photoelectrochemical performance of NiS-modified TiO2 nanorods with a surface charge accumulation facet

Photoelectrochemical (PEC) water splitting for hydrogen production technology is considered as one of the most promising solutions to energy shortage and environmental remediation. TiO2/NiS nanorod arrays were successfully prepared using hydrothermal deposition followed by the successive ionic layer adsorption and reaction (SILAR) method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and photoluminescence (PL) spectra characterization studies indicate the successful deposition of NiS on TiO2 NRs. The NiS deposition on TiO2 was optimized by controlling the impregnation cycle. The optimal sample exhibits a photocurrent density of 1.16 mA cm-2 at 0.6 V vs. Ag/AgCl, which is a 1.9-fold enhancement over that of pristine TiO2 nanorod arrays. The enhanced photoelectrochemical performance can be attributed to two aspects. On the one hand, the (101) crystal plane of rutile TiO2 is the facet where photogenerated holes accumulate and is an efficient active plane for the oxygen evolution reaction; on the other hand, NiS is a narrow band gap semiconductor, and its deposition on TiO2 nanorods can further promote the separation and transport of photogenerated charge carriers.

Long-term durability of metastable β-Fe2O3 photoanodes in highly corrosive seawater

Durability is one prerequisite for material application. Photoelectrochemical decomposition of seawater is a promising approach to produce clean hydrogen by using solar energy, but it always faces the problem of serious Cl^- corrosion. We find that the main deactivation mechanism of the photoanode is oxide surface reconstruction accompanied by the coordination of Cl^- during seawater splitting, and the stability of the photoanode can be effectively improved by enhancing the metal-oxygen interaction. Taking the metastable β-Fe₂O₃ photoanode as an example, Sn added to the lattice can enhance the M-O bonding energy and hinder the transfer of protons to lattice oxygen, thereby inhibiting excessive surface hydration and Cl^- coordination. Therefore, the bare Sn/β-Fe₂O₃ photoanode delivers a record durability for photoelectrochemical seawater splitting over 3000 h.

Boosting Pseudocapacitive Behavior of Supercapattery Electrodes by Incorporating a Schottky Junction for Ultrahigh Energy Density

Pseudo-capacitive negative electrodes remain a major bottleneck in the development of supercapacitor devices with high energy density because the electric double-layer capacitance of the negative electrodes does not match the pseudocapacitance of the corresponding positive electrodes. In the present study, a strategically improved Ni-Co-Mo sulfide is demonstrated to be a promising candidate for high energy density supercapattery devices due to its sustained pseudocapacitive charge storage mechanism. The pseudocapacitive behavior is enhanced when operating under a high current through the addition of a classical Schottky junction next to the electrode-electrolyte interface using atomic layer deposition. The Schottky junction accelerates and decelerates the diffusion of OH‒/K+ ions during the charging and discharging processes, respectively, to improve the pseudocapacitive behavior. The resulting pseudocapacitive negative electrodes exhibits a specific capacity of 2,114 C g-1 at 2 A g-1 matches almost that of the positive electrode's 2,795 C g-1 at 3 A g-1. As a result, with the equivalent contribution from the positive and negative electrodes, an energy density of 236.1 Wh kg-1 is achieved at a power density of 921.9 W kg-1 with a total active mass of 15 mg cm-2. This strategy demonstrates the possibility of producing supercapacitors that adapt well to the supercapattery zone of a Ragone plot and that are equal to batteries in terms of energy density, thus, offering a route for further advances in electrochemical energy storage and conversion processes.

Core-Shell Engineered WO3 Architectures: Recent Advances from Design to Applications

Ongoing efforts to design novel materials with efficient structure-property-performance relations prove challenging. Core-shell structures have emerged as novel materials with controlled production routes and highly tailorable properties that offer extensive advantages in advanced oxidation processing, particularly in photocatalysis and photoelectrochemical applications. WO₃ , which is an optoelectronically active semiconductor material, is a popular material in current studies in the field of photo(electro)catalysis. Considerable progress has been made using core-shell WO₃ architectures, which warrants an evaluation in terms of processing and preparedness for their use in versatile catalytic and energy storage applications. This paper presents an in-depth assessment of core-shell WO₃ architectures by highlighting the design challenges and protocols in powder and thin-film chemical processing. The development of specific core-shell designs for use in targeted applications, such as H₂ production, CO₂ reduction, wastewater treatment, batteries, supercapacitors, and sensing, is analyzed. The fundamental role of WO₃ in core-shell structures to enhance efficiency is also discussed, along with the limitations and improvement strategies. Further, the prospects of core-shell WO₃ architectures in energy conversion and environmental applications are suggested.