Xu-Dong Wang

Novel porous molybdenum tungsten phosphide hybrid nanosheets on carbon cloth for efficient hydrogen evolution

Nanostructural modification and chemical composition tuning are paramount to developing effective non-noble hydrogen evolution reaction (HER) catalysts for water splitting. Herein, we report a novel excellent porous molybdenum tungsten phosphide (Mo–W–P) hybrid nanosheet catalyst for hydrogen evolution, which is synthesized via in situ phosphidation of molybdenum tungsten oxide (Mo–W–O) hybrid nanowires grown on carbon cloth. The three-dimensional (3D) hierarchical hybrid electrocatalyst exhibits impressively high electrocatalytic activity with a low overpotential of 138 mV required to achieve a high current density of 100 mA cm−2 and a small Tafel slope of 52 mV dec−1 in 0.5 M H2SO4, which are significantly higher than those of single MoP nanosheets and WP2 nanorods. Such an outstanding performance of the Mo–W–P hybrid electrocatalyst is attributed to the 3D conductive scaffolds, porous nanosheet structure, and strong synergistic effect of W and Mo atoms in Mo–W–P, making it a very promising catalyst for hydrogen production. Our findings demonstrate that careful control over the morphology and composition of the electrocatalyst can achieve highly efficient hybrid electrocatalysts.

A CsPbBr3 Perovskite Quantum Dot/Graphene Oxide Composite for Photocatalytic CO2 Reduction

Halide perovskite quantum dots (QDs), primarily regarded as optoelectronic materials for LED and photovoltaic devices, have not been applied for photochemical conversion (e.g., water splitting or CO2 reduction) applications because of their insufficient stability in the presence of moisture or polar solvents. Herein, we report the use of CsPbBr3 QDs as novel photocatalysts to convert CO2 into solar fuels in nonaqueous media. Under AM 1.5G simulated illumination, the CsPbBr3 QDs steadily generated and injected electrons into CO2, catalyzing CO2 reduction at a rate of 23.7 μmol/g h with a selectivity over 99.3%. Additionally, through the construction of a CsPbBr3 QD/graphene oxide (CsPbBr3 QD/GO) composite, the rate of electron consumption increased 25.5% because of improved electron extraction and transport. This study is anticipated to provide new opportunities to utilize halide perovskite QD materials in photocatalytic applications.

Self-supported NiMoP2 nanowires on carbon cloth as an efficient and durable electrocatalyst for overall water splitting

Designing and exploring efficient and stable non-noble bifunctional catalysts by nanostructure modification and chemical composition tuning for water splitting is of critical importance for sustainable resources. Herein, pure phase nickel molybdenum phosphide (NiMoP2) nanowires on carbon cloth are successfully synthesized through a simple and highly reproducible in situ P/O exchange process. Such a NiMoP2 nanowire catalyst requires low overpotentials of 199 and 330 mV to obtain a high current density of 100 mA cm−2 towards the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, and is among the most active HER and OER electrocatalysts yet reported. The bifunctional NiMoP2 is used as both anode and cathode catalysts in a two-electrode water electrolysis configuration, which delivers a current density of 10 mA cm−2 under a potential of 1.67 V. Furthermore, the overall water-splitting of the bifunctional NiMoP2 nanowire catalyst is further driven by a dry battery with a nominal voltage of 1.5 V which exhibits excellent performance and durability in a strong alkaline electrolyte.

In situ formation of zinc ferrite modified Al-doped ZnO nanowire arrays for solar water splitting

Solar water splitting by photoelectrochemical (PEC) cells is emerged as a promising route for H2 production. However, thus far no single component material can fulfill all the requirements for high efficiency PEC behavior, especially for the photoanode which conducts the water oxidation, while constructing a composite photoelectrode can result in improved performance. Herein, a simple wet-chemical treatment method is introduced to in situ fabricate ZnFe2O4 onto conductive Al:ZnO nanowire arrays for solar-driven water splitting. Benefiting from the high conductivity of Al:ZnO and the visible-spectrum absorption of ZnFe2O4, such a host–guest structure has finally led to an excellent photoelectrochemical performance with low onset potential (VRHE = 0.38 V) and a photocurrent density of 1.72 mA cm−2 (VRHE = 1.23 V). Notably, the low onset potential gives this structure great potential for application in unassisted light-driven tandem-type PEC cells.

A formamidinium–methylammonium lead iodide perovskite single crystal exhibiting exceptional optoelectronic properties and long-term stability

Halide perovskite single crystal of cubic HC(NH2)2PbI3 (FAPbI3) having excellent optoelectronic properties, such as narrow bandgap, large absorption coefficient and superior thermal stability has caught a surge of attention as a promising material for production of high-performance optoelectronic devices. However, at room temperature, the self-transformation of cubic FAPbI3 perovskite phase to non-perovskite phase leaves a critical roadblock to its practical viability. Herein, a simple alloying strategy by mixing methylammonium with formamidinium is developed to stabilize the FAPbI3 perovskite phase, hence achieving a highly stable mixed cation MA0.45FA0.55PbI3 perovskite single crystal over a span of 14 months. The MA0.45FA0.55PbI3 single crystal exhibits exceptional optoelectronic properties like high carrier mobility of 271 ± 60 cm2 s−1 V−1 and long diffusion length up to 254 μm, which are twice the values for sole MAPbI3 or FAPbI3 crystals. In addition, the photodetector based on MA0.45FA0.55PbI3 single crystal exhibits low detection limit of about 1 nW cm−2, high ON–OFF ratio of ∼1000, short response time of less than 200 μs, and impressive stability under aging in dark for 4 months or continuous photo-switching test for 1000 s.

Large-Area Synthesis of a Ni2P Honeycomb Electrode for Highly Efficient Water Splitting

Transition metal phosphides have recently been regarded as robust, inexpensive electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Thus far, tremendous scientific efforts have been applied to improve the catalytic activity of the catalyst, whereas the scale-up fabrication of morphology-controlled catalysts while maintaining their desired performance remains a great challenge. Herein, we present a facile and scalable approach to fabricate the macroporous Ni2P/nickel foam electrode. The obtained electrocatalyst exhibits superior bifunctional catalytic activity and durability, as evidenced by a low overpotential of 205 and 300 mV required to achieve a high current density of 100 mA cm-2 for HER and OER, respectively. Such a spray-based strategy is believed to widely adapt for the preparation of electrodes with uniform macroporous structures over a large area (e.g., 100 cm2), which provides a universal strategy for the mass fabrication of high performance water-splitting electrodes.

3D Cathodes of Cupric Oxide Nanosheets Coated onto Macroporous Antimony-Doped Tin Oxide for Photoelectrochemical Water Splitting.

Cupric oxide (CuO), a narrow-bandgap semiconductor, has a band alignment that makes it an ideal photocathode for the renewable production of solar fuels. However, the photoelectrochemical performance of CuO is limited by its poor conductivity and short electron diffusion lengths. Herein, a three-dimensional (3D) architecture consisting of CuO nanosheets supported onto transparent conducting macroporous antimony-doped tin oxide (mpATO@CuONSs) is designed as an excellent photocathode for promoting the hydrogen evolution reaction (HER). Owing to the 3D structure affording superior light-harvesting characteristics, large contact areas with the electrolyte, and highly conductive pathways for separation and transport of charge carriers, the mpATO@CuONSs photocathode produces an impressively high photocurrent density of -4.6 mA cm-2 at 0 V versus the reversible hydrogen electrode (RHE), which is much higher than that of the CuONSs array onto planar FTO glass (-1.9 mA cm-2 ).

Iron-assisted engineering of molybdenum phosphide nanowires on carbon cloth for efficient hydrogen evolution in a wide pH range

Exploration of active, cost-effective, and stable non-noble electrocatalysts for efficient hydrogen evolution is essential for sustainable energy systems. In this study, we report the synthesis of molybdenum phosphide nanowires on carbon cloth (MoP NW/CC) by a facile iron-assisted strategy; the as-obtained MoP NW/CC is a robust hydrogen evolution catalyst with high activity. Results reveal that the added iron can promote the upward growth of ferrum molybdenum oxide (Fe–Mo–O) nanowire precursor on carbon cloth and morphological maintenance during the in situ gas–solid phosphidation process; thus, iron plays a key role in engineering the morphology of the catalysts. As a novel 3D hydrogen evolution cathode, the as-obtained MoP NW/CC electrode exhibits a low onset potential of 72 mV, low overpotential of 173 mV for high current density of 100 mA cm−2, a small Tafel slope of 53.3 mV dec−1, and superior durability in an acidic electrolyte. Additionally, this electrode displays considerable HER activity and promising stability in alkaline and neutral media. This outstanding HER activity for MoP NW/CC can be ascribed to its unique nanowire morphology with a large surface area exposing ample active sites and superior charge transport kinetics. Importantly, in our study, a facile and effective approach has been developed for regulating the morphology of transition-metal phosphides.