Lattice-disordered high-entropy metal hydroxide nanosheets as efficient precatalysts for bifunctional electro-oxidation

Superhydrophilic/superaerophobic CoP/CoMoO4 multi-level hierarchitecture electrocatalyst for urea-assisted hydrogen evolution reaction in alkaline media

Utilizing the thermodynamically favorable urea oxidation reaction instead of the anodic oxygen precipitation reaction is an alternative pathway for the energy-saving hydrogen production. Therefore, it is significant to explore advanced electrocatalysts for both HER and UOR. In this work, a dendritic heteroarchitectures of 2D CoMoO4 nanosheets deposited on 1D CoP nanoneedles (CoP/CoMoO4-CC) was fabricated as bifunctional electrocatalyst. 1D CoP nanostructure with fast charge transport pathways and 2D CoMoO4 nanostructure with large specific surface area and short paths for electron/mass transport. The unique morphology endows the superhydrophilic and superaerophobic properties, allowing for the rapid contact with the reactants and rapid removal of surface-generated gases. As a result, the CoP/CoMoO4-CC shows efficient bifunctional activity. This work offers a new avenue to rationally design bifunctional electrocatalysts for large-scale practical hydrogen production.

Amorphous conversion in pyrolytic symmetric trinuclear nickel clusters trigger trifunctional electrocatalysts

The pursuit of multifunctional electrocatalysts holds significant importance due to their comprehension of material chemistry. Amorphous materials are particularly appealing, yet they pose challenges in terms of rational design due to their structural disorder and thermal instability. Herein, we propose a strategy that entails the tandem (low-temperature/250-350 °C) pyrolysis of molecular clusters, enabling preservation of the local short-range structures of the precursor Schiff base nickel (Ni3[2(C21H24N3Ni1.5O6)]). The temperature-dependent residuals demonstrate exceptional activity and stability for at least three distinct electrocatalytic processes, including the oxygen evolution reaction (η10 = 197 mV), urea oxidation reaction (η10 = 1.339 V), and methanol oxidation reaction (1358 mA cm-2 at 0.56 V). Three distinct nickel atom motifs are discovered for three efficient electrocatalytic reactions (Ni1 and Ni1' are preferred for UOR/MOR, while Ni2 is preferred for OER). Our discoveries pave the way for the potential development of multifunctional electrocatalysts through disordered engineering in molecular clusters under tandem pyrolysis.

Constructing Sequential Type II Heterojunction CQDs/Bi2S3/TiNbO Photoanode with Superior Charge Transfer Capability Toward Stable Photoelectrochemical Water Splitting

Efficient charge transfer and light-trapping units are pivotal prerequisites in the realm of Ti-based photoanode photoelectrochemical (PEC) water splitting. In this work, we successfully synthesized a ternary carbon quantum dots/Bi2S3 quantum dots/Nb-doped TiO2 nanotube arrays (CQDs/Bi2S3/TiNbO) composite photoanode for PEC water splitting. CQDs/Bi2S3/TiNbO composite photoanode exhibited a considerably elevated photocurrent density of 8.80 mA cm-2 at 1.23 V vs the reversible hydrogen electrode, which was 20.00 times better than that of TiO2 (0.44 mA cm-2). Furthermore, the CQDs/Bi2S3/TiNbO composite photoanode attested to exceptional stability, maintaining 92.54% of its initial current after 5 h of stability measurement. Nb-doping boosted the electrical conductivity, facilitating charge transfer at the solid-liquid interface. Moderate amounts of Bi2S3 quantum dots (QDs) and CQDs deposited on TiNbO provided abundant active sites for the electrolyte-photoanode interaction. Simultaneously, Bi2S3 QDs and CQDs synergistically functioned as light-trapping units to broaden the light absorption range from 396 to 530 nm, stimulating increased carrier generation within the composite photoanode. In comparison with pristine TiO, CQDs/Bi2S3/TiNbO photoanodes possessed a superior ability to promote interfacial reactions. This study may provide a strategy for developing high-performance Ti-based photoanodes with efficient charge transfer and light trapping units for highly driving solar-to-hydrogen conversion.

Controlled establishment of advanced local high-entropy NiCoMnFe-based layered double hydroxide for zinc batteries and low-temperature supercapacitors

The development of high-performance electrodes is essential for improving the charge storage performance of rechargeable devices. In this study, local high-entropy C, N co-doped NiCoMnFe-based layered double hydroxide (C/N-NiCoMnFe-LDH, C/N-NCMF) were designed using a novel method. Multi-component synergistic effects can dramatically modulate the surface electron density, crystalline structure, and band-gap of the electrode. Thus, the electrical conductivity, electron transfer, and affinity for the electrolyte can be optimized. Additionally, the C/N-NCMF yielded a high specific capacitance (1454F·g-1) at 1 A·g-1. The electrode also exhibited excellent cycling stability, with 62 % capacitance retention after 5000 cycles. Moreover, the assembled Zn||C/N-NCMF battery and the C/N-NCMF//AC hybrid supercapacitor yielded excellent energy densities of 63.1 and 35.4 Wh·kg-1 at power densities of 1000 and 825 W·kg-1, and superior cycling performance with 69 % and 88.7 % capacitance retention after 1000 and 30,000 cycles, respectively. Furthermore, the electrode maintained high electrochemical activity and stability and ensured high energy density, power density, and cycling stability of the rechargeable devices even at a low temperature (-20 °C). This study paves a new pathway for regulating the electrochemical performance of LDH-based electrodes.

Understanding the role of solvents in bottom-up synthesis of multi-element hydroxides

Here we report a comparative study on the bottom-up synthesis of multi-element hydroxides composed of Mg, Al, Fe and Zn cations to understand the role of solvents. Two common solvents, water and ethylene glycol, a typical polyol, are used. The polyol-derived MgAlFeZn-OH are nanosheets with homogeneous elemental distribution, while the hydrothermal-derived MgAlFeZn-OH are mixtures of plate-like hydroxide layers and rod-like spinel oxides. The coordinating properties and the high viscosity of the ethylene glycol provide the possibility to mediate the hydrolysis rates and to control the particle growth. The high specific surface area of the polyol-derived multi-element hydroxide nanosheets (352.4 m2 g-1) guarantees them as excellent adsorbents for adsorbing anionic dyes in aqueous solution.

High-entropy wire-on-sheet nanoarray catalyst with boosted pre-oxidation for efficient oxygen evolution reaction

Herein, a septenary NiCoZnFeCuMnCe hydroxide nanoarray catalyst with a unique wire-on-sheet morphology and high-entropy feature was fabricated, which exhibits boosted pre-oxidation behavior and synergistically enhanced catalytic activity and durability towards the oxygen evolution reaction.

Carbon cloth supporting spinel CuMn0.5Co2O4 nanoneedles with the regulated electronic structure by multiple metal elements as catalysts for efficient oxygen evolution reaction

Developing transition metal oxide catalysts to replace the noble metal oxide catalysts for efficient oxygen evolution reaction (OER) is essential to promote the practical application of water splitting. Herein, we designed and constructed the carbon cloth (CC) supporting spinel CuMn_0.5Co₂O₄ nanoneedles with regulated electronic structure by multiple metal elements with variable chemical valences in the spinel CuMn_0.5Co₂O₄. The carbon cloth not only provided good conductivity for the catalytic reaction but also supported the well-standing spinel CuMn_0.5Co₂O₄ nanoneedles arrays with a large special surface area. Meanwhile, the well-standing nanoneedles arrays and mesoporous structure of CuMn_0.5Co₂O₄ nanoneedles enhanced their wettability and facilitated access for electrolyte to electrochemical catalysis. Besides, the regulated electronic structure and generated oxygen vacancies of CuMn_0.5Co₂O₄/CC by multiple metal elements improved the intrinsic catalytic activity and the durability of OER activity. Profiting from these merits, the CuMn_0.5Co₂O₄/CC electrode exhibited superior OER activity with an ultralow overpotential of 189 mV at the current density of 10 mA⋅cm^-2 and a smaller Tafel slope of 64.1 mV⋅dec^-1, which was competitive with the noble metal oxides electrode. And the CuMn_0.5Co₂O₄/CC electrode also exhibited long-term durability for OER with 95.3% of current retention after 1000 cycles. Therefore, the competitive OER activity and excellent cycling durability suggested that the CuMn_0.5Co₂O₄/CC electrode is a potential candidate catalyst for efficient OER.