Quasi-layer Co2P-polarized Cu3P nanocomposites with enhanced intrinsic interfacial charge transfer for efficient overall water splitting

Structural Design of Nickel Hydroxide for Efficient Urea Electrooxidation

Urea stands as a ubiquitous environmental contaminant. However, not only does urea oxidation reaction technology facilitate energy conversion, but it also significantly contributes to treating wastewater rich in urea. Furthermore, urea electrolysis has a significantly lower theoretical potential (0.37 V) compared to water electrolysis (1.23 V). As an electrochemical reaction, the catalytic efficacy of urea oxidation is largely contingent upon the catalyst employed. Among the plethora of urea oxidation electrocatalysts, nickel-based compounds emerge as the preeminent transition metal due to their cost-effectiveness and heightened activity in urea oxidation. Ni(OH)2 is endowed with manifold advantages, including structural versatility, facile synthesis, and stability in alkaline environments. This review delineates the recent advancements in Ni(OH)2 catalysts for electrocatalytic urea oxidation reaction, encapsulating pivotal research findings in morphology, dopant incorporation, defect engineering, and heterogeneous architectures. Additionally, we have proposed personal insights into the challenges encountered in the research on nickel hydroxide for urea oxidation, aiming to promote efficient urea conversion and facilitate its practical applications.

A pillar-layered Ni2P-Ni5P4-CoP array derived from a metal-organic framework as a bifunctional catalyst for efficient overall water splitting

Interfacial engineering emerges as a potent strategy for regulating the catalytic reactivity of metal phosphides. Developing a facile and cost-effective method to construct bifunctional metal phosphides for highly efficient electrochemical overall water splitting remains an essential and challenging issue. Here, a multiphase transition metal phosphide is constructed through the direct phosphorization of a Ni-Co metal-organic framework grown on nickel foam (Ni-Co-MOF/NF), which is prepared by utilizing nickel foam as conductive substrate and nickel source. The resulting transition metal phosphide manifests a pillar-layered morphology, wherein CoP, Ni2P, and Ni5P4 nanoparticles are embedded within each carbon sheet and these carbon sheets assemble into a pillar-shaped structure on the nickel foam (Ni2P-Ni5P4-CoP-C/NF). The heterogeneous Ni2P-Ni5P4-CoP-C/NF with multiple interfaces serves as a highly efficient bifunctional electrocatalyst with overpotentials of -100 mV and 293 mV in the hydrogen evolution reaction and oxygen evolution reaction, respectively, at 50 mA cm-2 in alkaline media. This superior catalytic performance should mainly be ascribed to its enriched active centers and multiphase synergy. When directly applied for alkaline overall water splitting, the Ni2P-Ni5P4-CoP-C/NF couple demonstrates satisfactory activity (1.55 V @10 mA cm-2) along with sustained durability over 18 hours. This method brings fresh enlightenment to the economical and controllable preparation of multi-metal phosphides for energy conversion.

Electrochemical tuning of a Cu3P/Ni2P hybrid for a promoted hydrogen evolution reaction

Developing novel and high performance electrocatalysts for use in hydrogen evolution reactions (HER) as substitutes for noble metal based electrocatalysts is imperative and, so far, has been a challenge. Herein, a self-supported Cu₃P/Ni₂P hybrid on nickel foam (Cu₃P/Ni₂P@NF) is prepared by a simple galvanic replacement reaction coupled with phosphorization. Subsequently, Cu₃P/Ni₂P@NF is modified by conducting cyclic voltammetry scans in 0.5 M H₂SO₄ solution. Interestingly, after electrochemical tuning, the as-prepared Cu₃P/Ni₂P@NF exhibits significantly enhanced HER activity. Particularly, the resultant Cu₃P/Ni₂P@NF catalyst after 4000 cycles exhibits superior catalytic activity and long-term stability for HER with an overpotential of only 67 mV at the current density of 10 mA cm^-2, and a low Tafel slope of 43.9 mV dec^-1. The improved HER performance is attributed to the increased intrinsic activity of the Cu₃P/Ni₂P@NF with its optimized crystal and electronic structure, as well as an increased number of accessible active sites due to surface dissolution and recrystallization induced by electrochemical modification.

Amorphous NiCuFeP@Cu3P nanoarray for an efficient hydrogen evolution reaction

Transition metal phosphides are considered as ideal alternatives for noble metal catalysts for hydrogen evolution reactions. In this study, amorphous NiCuFeP nanosheets are uniformly coated on self-supporting Cu3P nanowire array...

Nanostructured metal phosphides: from controllable synthesis to sustainable catalysis

Metal phosphides (MPs) with unique and desirable physicochemical properties provide promising potential in practical applications, such as the catalysis, gas/humidity sensor, environmental remediation, and energy storage fields, especially for transition metal phosphides (TMPs) and MPs consisting of group IIIA and IVA metal elements. Most studies, however, on the synthesis of MP nanomaterials still face intractable challenges, encompassing the need for a more thorough understanding of the growth mechanism, strategies for large-scale synthesis of targeted high-quality MPs, and practical achievement of functional applications. This review aims at providing a comprehensive update on the controllable synthetic strategies for MPs from various metal sources. Additionally, different passivation strategies for engineering the structural and electronic properties of MP nanostructures are scrutinized. Then, we showcase the implementable applications of MP-based materials in emerging sustainable catalytic fields including electrocatalysis, photocatalysis, mild thermocatalysis, and related hybrid systems. Finally, we offer a rational perspective on future opportunities and remaining challenges for the development of MPs in the materials science and sustainable catalysis fields.

Enhanced Oxygen Evolution Reaction Activity of a Co2P@NC-Fe2P Composite Boosted by Interfaces Between a N-Doped Carbon Matrix and Fe2P Microspheres

Constructing highly efficient and low-cost transition-metal-based electrocatalysts with a large number of interfaces to increase their active site densities constitutes a major advancement in the development of water-splitting technology. Herein, a bimetallic phosphide composite (Co₂P@NC-Fe₂P) is successfully synthesized from a ferric hydroxyphosphate-zeolitic imidazolate framework hybrid precursor (FeHP-ZIF-67). Benefitting from morphology and composition regulations, the FeHP-ZIF-67 precursor is prepared by a room-temperature solution synthesis method, which exhibits an optimal morphology, where FeHP microspheres are coated with excess ZIF-67 nanoparticles. During the annealing of FeHP-ZIF-67, FeHP serves as a source of phosphorus to form Fe₂P and Co₂P simultaneously, where Co₂P nanoparticles coated with an N-doped carbon (NC) matrix derived from ZIF-67 are partially adsorbed onto the surface of Fe₂P microspheres, thereby forming numerous NC-Fe₂P interfaces. The optimal Co₂P@NC-Fe₂P composite has an overpotential of 260 mV at a current density of 10 mA cm^-2, a small Tafel slope of 41 mV dec^-1, and long-term stability of over 35 h in an alkaline medium for oxygen evolution reactions (OERs). Such a superior OER performance is attributed to the active NC-Fe₂P interfaces in the Co₂P@NC-Fe₂P composite. This work provides a new strategy to optimize transition-metal phosphides with effective interfaces for OER electrocatalysis.

Efficient bifunctional catalysts for overall water splitting: porous Fe-Mo oxide hybrid nanorods

Efficient and inexpensive bifunctional catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are essential for water splitting. Herein, we successfully prepare porous Fe-Mo oxide hybrid nanorods through a hydrothermal method followed by annealing at high temperature. They exhibit excellent catalytic activity for OER and HER in alkaline media, and produce a current density of 10 mA cm-2 at overpotentials of 200 and 66 mV. Besides, they work as bifunctional electrode materials for overall water splitting, achieving a current density of 10 mA cm-2 at a voltage of 1.52 V, and maintaining a current density of 60 mA cm-2 for 60 h. The unique morphology with self-supported structure can expose more active sites and facilitate charge transfer, and is not easy to peel off, thus it improves the catalytic activity and stability. This work therefore provides a valuable route for designing and fabricating inexpensive and high-performance catalytic materials for overall water splitting.

Highly enhanced bifunctional electrocatalytic activity of mixed copper–copper oxides on nickel foam via composition control

Fabricating Cu₂O–CuO and CuO directly on the conducting nickel foam resulted in highly enhanced OER and HER electrocatalytic activity in an alkaline medium, respectively.

Hydrothermal synthesis of polydopamine-functionalized cobalt-doped lanthanum nickelate perovskite nanorods for efficient water oxidation in alkaline solution

Perovskite oxides have attracted great attention recently for their low cost and high intrinsic activity in the electrochemical oxygen evolution reaction (OER). In this work, we synthesized highly efficient OER electrocatalysts in alkaline solution by carbonization of polydopamine (PDA)-functionalized cobalt-doped lanthanum nickelate perovskite nanorod (La₅Ni₃Co₂) complexes. The calcination temperature and molar ratio for La, Ni, and Co were optimized. The as-prepared complex with a molar ratio of 5 : 3 : 2 (La : Ni : Co) and a calcination temperature of 500 °C displayed enhanced OER activity and excellent durability. In 1.0 M KOH, the overpotential of the as-prepared catalyst at a current density of 10 mA cm^-2 was 0.360 V, which is comparable to those of noble metal-based materials or perovskite-based materials. The Tafel slope is 48.1 mV dec^-1, which is smaller than those of prepared composites. The satisfactory oxygen evolution activity could be attributed to the increased Co₃O₄, O₂^2-/O^-, pyridine N, and quaternary N species after calcination treatment, and the improved amount of Ni³⁺ during the OER process, as well as the high surface area and electrochemical surface area.

Regulating the electron density of dual transition metal sulfide heterostructures for highly efficient hydrogen evolution in alkaline electrolytes

Exploring highly effective electrocatalysts with heterostructures is significant for sustainable hydrogen production by the hydrogen evolution reaction (HER). However, there are still challenges in improving the HER activities of the heterostructures to achieve efficient hydrogen production. Here, nitrogen-decorated dual transition metal sulphide heterostructures (N-NiS/MoS₂) were constructed with an enhanced HER performance in alkaline electrolytes. These novel N-NiS/MoS₂ heterostructures exhibited a low overpotential of 71 mV (10 mA cm^-2), small Tafel slope of 79 mV dec^-1 and favorable stability. In particular, the experimental and theoretical calculation results consistently demonstrated that the introduction of nitrogen can effectively tune the electronic structure of the heterostructures. Furthermore, the synergistic effect between dual-active components N-NiS and N-MoS₂ in the N-NiS/MoS₂ heterostructures effectively promoted water dissociation and hydrogen formation, leading to remarkable increase in the HER performance in an alkaline medium. This work provides a valuable avenue for the rational modulation of the electronic structure of heterostructures by hetero-atoms for highly efficient HER catalysts.