Carbon-encapsulated Co(2)P/P-modified NiMoO(4) hierarchical heterojunction as superior pH-universal electrocatalyst for hydrogen production

Enhanced electrocatalytic water splitting activity by modulating the catalytic microenvironment with incorporated rhenium atoms in metal organic frameworks derived cobalt phosphide

Modulating the catalytic microenvironment has emerged as a highly effective strategy for developing high-performance catalysts. In this study, a microenvironment modulation strategy is successfully implemented by incorporating rhenium (Re) atoms into metal organic frameworks (MOFs)-derived cobalt phosphide (Co2P). This results in the production of a high-performance electrocatalyst of Re-Co2P for overall water splitting (OWS). Owing to the incorporated Re atoms, the catalytic microenvironment is effectively regulated, and the conductivity and electron transfer are improved as well. As a result, the optimized Re-Co2P catalyst exhibits outstanding catalytic activities, manifested as the low overpotentials of 57 and 235 mV under 10 mA cm-2 for hydrogen and oxygen evolution reactions, and a small cell voltage of 1.50 V under 10 mA cm-2 for OWS. Experimental characterizations and density functional theory calculations reveal that Re incorporation in Co2P regulates the electronic structure, facilitates the charge transfer, and optimizes the Gibbs free energy, thereby improving the water splitting efficiency. This work demonstrates an efficient strategy to construct OWS electrocatalysts by regulating the catalytic microenvironment through the incorporation of metal atoms into MOFs-derived materials.

Synergistic design of hierarchical and heterostructural P-NiMoO4@Net-like Ni2P for enhanced hydrogen evolution electrocatalysis

Hierarchical structure design and heterostructure engineering are effective strategies for enhancing hydrogen evolution reaction (HER) performance, yet their synergistic integration remains underexplored. In this work, a novel hierarchical P-NiMoO4@Net-like Ni2P heterostructure HER electrocatalyst was prepared via a two-step hydrothermal method followed by low-temperature phosphorization. The three-dimensional net like Ni2P was closely integrated with one-dimensional phosphorus-doped NiMoO4 micro/nanorod arrays, enabling hierarchical structural assembly and the formation of synergistic heterointerfaces. The hierarchical structure significantly increased active site exposure, with a double-layer capacitance of 254.4 mF cm-2, more than five times that of single-component Ni2P (48.4 mF cm-2). Density functional theory calculations revealed that the heterostructure lowered the d-band center of active Ni3 sites and optimized the hydrogen adsorption energy, thereby enhancing HER activity. The P-NiMoO4@Net-like Ni2P catalyst exhibited an alkaline HER overpotential of 49 mV at a current density of 10 mA cm-2. It also maintained stable operation for 100 h at 10mA cm-2 and 120 h at 100mA cm-2. This study demonstrates the potential of integrating hierarchical and heterostructural strategies, providing a reference for advanced nanostructured catalyst development.

Dual-metal heterogeneous electrode enabling efficient co-electrosynthesis of adipic acid and hydrogen

The electrochemical oxidation of cyclohexanone to produce adipic acid (AA), coupled with hydrogen (H2) production, represents a promising strategy. However, the development of low-cost and high-performance electrodes remains a significant challenge. Herein, we present Ni@Cu dual-metal heterogeneous material as a proof of concept, demonstrating its potential for efficient co-electrosynthesis of adipic acid and H2. The Ni@Cu material, featuring abundant heterogeneous interfaces, is grown on copper foam (CF) through a straightforward electrochemical reconstitution strategy. This approach enhances the exposure of catalytic active sites, improves interfacial charge transfer, and accelerates reaction kinetics during electrolysis. As a result, the Ni@Cu/CF electrode achieves low potentials of -172 mV vs. RHE and 1.55 V vs. RHE at 100 mA cm-2 for the hydrogen evolution reaction (HER) and cyclohexanone oxidation reaction (COR), respectively. The assembled HER||COR electrolyzer delivers a high adipic acid yield (1.15 mmol h-1 at 250 mA cm-2) and a maximum Faradaic efficiency (FE) of 88 % at 100 mA cm-2. It also achieves a high FE for H2 (over 96 % at 250 mA cm-2) and demonstrates excellent co-electrolysis stability for over 100 h. In-situ spectroscopy confirms that the formation of heterogeneous Ni@Cu facilitates the generation of active species and accelerates their kinetic transformation into adipic acid.

Synthesis of IrCu/Co3O4 hybrid nanostructures and their enhanced catalytic properties toward oxygen evolution reaction under both acidic and alkaline conditions

Oxygen evolution reaction (OER) is a half-reaction that occurs at the anode during water electrolysis, and owing to its slow kinetics, it is the rate-limiting step in the process. Alloying with transition metal and combining with transition metal oxide supports are effective methods for modifying the electronic structure of noble metal catalysts and improving their catalytic properties. In this study, we synthesized IrCu/Co3O4 hybrid nanostructures by attaching IrCu alloy nanoparticles onto Co3O4 nanosheets. The electron transfer from Ir to Co altered the electronic structure of IrCu and became a crucial factor for the enhanced catalytic activity of the IrCu/Co3O4 hybrid nanostructure in the OER reaction. Additionally, the hybrid nanostructure demonstrated excellent catalytic stability under both alkaline and acidic conditions (135 and 60 h at 10 mA cm-2, respectively) due to its combination with Co3O4 nanosheets. The present work paves a new approach for the design and construction of efficient pH-universal electrocatalysts for OER.

Enhanced hydrogen evolution reaction activity through samarium-doped nickel phosphide (Ni2P) electrocatalyst

Hydrogen evolution reaction (HER) stands out among conventional hydrogen production processes by featuring excellent advantages. However, the uncompetitive production cost due to the low energy efficiency has hindered its development, necessitating the introduction of cost-effective electrocatalysts. In this study, we introduced samarium doping as a high-potential approach to improve the electrocatalytic properties of nickel phosphide (Ni2P) for efficient HER. Samarium-doped Ni2P was synthesized via a facile two-step vapor-solid reaction technique. Different physical and electrochemical analyses showed that samarium doping significantly improved pure Ni2P characteristics, such as particle size, specific surface area, electrochemical hydrogen adsorption, intrinsic activity, electrochemical active surface area, and charge transfer ability in favor of HER. Namely, Ni2P doped with 3%mol of samarium (Sm0.03Ni2P) with a Tafel slope of 67.8 mV/dec. and overpotential of 130.6 mV at a current density of 10 mA/cm2 in 1.0 M KOH solution exhibited a notable performance, suggesting Sm0.03Ni2P and samarium doping as a remarkable electrocatalyst and promising promoter for efficient HER process, respectively.

A hierarchical CoSx/Ni(OH)2 heterostructure as a bifunctional electrocatalyst for urea-assisted energy-efficient hydrogen production

We report hierarchical CoSx/Ni(OH)2/NF heterostructure nanorod arrays, which manifest superior bifunctional catalytic activities for the HER and UOR due to amorphous Ni(OH)2, synergistic effect of multiple components and self-supported structure. The CoSx/Ni(OH)2/NF-based urea electrolyzer requires a low cell voltage of 1.485 V to deliver 10 mA cm-2, which is obviously lower than that needed in water electrolysis.

A High-Performance Cr2O3/CaCO3 Nanocomposite Catalyst for Rapid Hydrogen Generation from NaBH4

This study aims to prepare new nanocomposites consisting of Cr2O3/CaCO3 as a catalyst for improved hydrogen production from NaBH4 methanolysis. The new nanocomposite possesses nanoparticles with the compositional formula Cr2-xCaxO3 (x = 0, 0.3, and 0.6). These samples were prepared using the sol-gel method, which comprises gelatin fuel. The structure of the new composites was studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, environmental scanning electron microscopy (ESEM), and X-ray spectroscopy (XPS). The XRD data showed the rhombohedral crystallinity of the studied samples, and the average crystal size was 25 nm. The FTIR measurements represented the absorption bands of Cr2O3 and CaO. The ESEM micrographs of the Cr2O3 showed the spherical shape of the Cr2O3 nanoparticles. The XPS measurements proved the desired oxidation states of the Cr2-xCaxO3 nanoparticles. The optical band gap of Cr2O3 is 3.0 eV, and calcium doping causes a reduction to 2.5 and 1.3 eV at 15.0 and 30.0% doping ratios. The methanolysis of NaBH4 involved accelerated H2 production when using Cr2-xCaxO3 as a catalyst. Furthermore, the Cr1.7Ca0.3O3 catalyst had the highest hydrogen generation rate, with a value of 12,750 mL/g/min.

Interfacial engineering of CoP/CoS2 heterostructure for efficiently electrocatalytic pH-universal hydrogen production

The design and development of high-performance, low-cost catalysts with long-term durability are crucial for hydrogen generation from water electrolysis. Interfacial engineering is an appealing strategy to boost the catalytic performance of electrode materials toward hydrogen evolution reaction (HER). Herein, we report a simple phosphidation followed by sulfidation treatment to construct heterogeneous cobalt phosphide-cobalt sulfide nanowire arrays on carbon cloth (CoP/CoS2/CC). When evaluated as catalysts toward the HER, the resultant CoP/CoS2/CC exhibits efficient pH-universal hydrogen production due to the heterostructure, synergistic contribution of CoP and CoS2, and conductive substrate. To attain a current density of 10 mA cm-2, overpotentials of only 111.2, 58.1, and 182.9 mV for CoP/CoS2/CC are required under alkaline, acidic, and neutral conditions, respectively. In particular, the as-prepared CoP/CoS2/CC shows markedly improved HER electroactivity in 1.0 M KOH, even outperforming commercial Pt-C/CC at a current density of >50 mA cm-2. In addition, the self-assembled CoP/CoS2||NiFe layered double hydroxide electrolyzer demonstrates efficient catalytic performance and long-time stability, excelling the benchmark Pt-C||IrO2. These findings indicate an effective pathway for the fabrication of high-performance heterogeneous electrocatalysts for hydrogen production in the future.

Anion-modulated CoP electrode as bifunctional electrocatalyst for anion-exchange membrane hydrazine-assisted water electrolyser

The hydrazine oxidation reaction (HzOR) is considered as a promising alternative process of the oxygen evolution reaction (OER) to realize more energy-efficient hydrogen generation. However, the lack of highly active bifunctional catalysts poses a huge challenge to this strategy. In this work, we report a novel and universal electrodeposition strategy to rationally synthesize a self-supporting electrode. The utilization of ammonium fluoride helps to modulate not only the morphology of CoP, but also the synchronous formation of an anion-modified structure, leading to an excellent bifunctional performance. The optimal F-CoP/CF exhibits small potentials of -90 mV and 41 mV at 1 A cm-2, high stability and low Tafel slopes of 28 mV dec-1 and 3.26 mV dec-1 for the HER and HzOR, respectively. The highly efficient and stable bifunctional activity of F-CoP/CF can be further confirmed in an anion-exchange membrane hydrazine-assisted water electrolyzer (0.49 V at 1 A cm-2). Utilizing the density functional theory calculations, the optimized adsorption energy of water molecules and hydrogen intermediates of the HER as well as the rate-determining step of the HzOR are demonstrated for the F-CoP.

Phosphorus-Modified Amorphous High-Entropy CoFeNiCrMn Compound as High-Performance Electrocatalyst for Hydrazine-Assisted Water Electrolysis

Exploiting highly active and bifunctional catalysts for both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) is a prerequisite for the hydrogen acquisition. High-entropy materials have received widespread attention in catalysis, but the high-performance bifunctional electrodes are still lacking. Herein, a novel P-modified amorphous high-entropy CoFeNiCrMn compound is developed on nickel foam (NF) by one-step electrodeposition strategy. The achieved CoFeNiCrMnP/NF delivers remarkable HER and HzOR performance, where the overpotentials as low as 51 and 268 mV are realized at 100 mA cm-2 . The improved cell voltage of 91 mV is further demonstrated at 100 mA cm-2 by assessing CoFeNiCrMnP/NF in the constructed hydrazine-assisted water electrolyser, which is almost 1.54 V lower than the HER||OER system. Experimental results confirm the important role of each element in regulating the bifuncational performance of high-entropy catalysts. The main influencing elements seem to be Fe and Ni for HER, while the P-modification and Cr metal may contribute a lot for HzOR. These synergistic advantages help to lower the energy barriers and improve the reaction kinetics, resulting in the excellent bifunctional activity of the CoFeNiCrMnP/NF. The work offers a feasible strategy to develop self-supporting electrode with high-entropy materials for overall water splitting.

Electronic interaction of ruthenium species on bimetallic phosphide for superior electrocatalytic hydrogen generation

The exploitation of high-performance electrocatalysts to achieve the economic electrocatalytic hydrogen evolution reaction (HER) is significant in generating H2 fuel. Enhancing the activity of the carrier catalyst by modifying trace precious metals is one of the important strategies. Herein, a hybrid material is developed by incorporating trace Ru species into a bimetallic phosphide (NiCoP) matrix on nickel foam (NF), showing a superior catalytic activity for HER. The Ru-NiCoP/NF hybrid material has plenty of heterointerfaces, improved electronic interaction, and small interfacial charge transfer resistance, improving the reaction kinetics of the HER. Remarkable, the Ru-NiCoP/NF provides a low overpotential of 96 mV at the current density of 50 mA cm-2 and high stability in 1.0 M KOH solution presenting a promising potential for hydrogen production. In addition, the Ru-NiCoP/NF sample exhibits the highest TOF value of 0.54 s-1 at an overpotential of 100 mV, which outperforms the commercial Ru/C catalyst. This study offers a promising approach for the synthesis of other precious metal supported hybrid materials.