Carbon supported nickel phosphide as efficient electrocatalyst for hydrogen and oxygen evolution reactions

Hydrogen production through water splitting is an efficient and green technology for fulfilling future energy demands. Carbon nanotubes (CNT) supported Ni₂P has been synthesized through a simpler hydrothermal method. Ni₂P/CNT has been employed as efficient electrocatalysts for hydrogen and oxygen evolution reactions in acidic and alkaline media respectively. The electrocatalyst has exhibited low overpotential of 137 and 360 mV for hydrogen and oxygen evolution reactions respectively at 10 mA cm^?2. Lower Tafel slopes, improved electrochemical active surface area, enhanced stability have also been observed. Advantages of carbon support in terms of activity and stability have been described by comparing with unsupported electrocatalyst.     

Magnetic metal phosphide nanorods as effective hydrogen-evolution electrocatalysts

Efficient and economical hydrogen evolution reaction (HER) from water splitting holds a bright prospect for clean energy. Replacement of expensive Pt-based catalysts with earth-abundant catalysts is beneficial for this field. In this study, nanoscale magnetic metal phosphides including Co₂P, Co_1.33Ni_0.67P and Ni₂P nanorods are synthesized by a facile solution method. Their HER activities and stabilities on glassy carbon and Ti electrodes are investigated. The Co₂P nanorods deposited on glassy carbon electrodes are found to show higher activity and better reversibility than the C_o1.33Ni_0.67P and Ni₂P counterparts. Nevertheless, the Co_1.33Ni_0.67P and Ni₂P samples on Ti electrodes gain a significant activity promotion after annealing in H₂/Ar atmosphere. Investigation of the Tafel curves shows that the Co₂P nanorods on glassy carbon have the lowest Tafel slope while their exchange current density on Ti electrode exhibits a high value which is comparable to that of Pt electrode. Furthermore, the cyclic voltammetric tests show that the reversibility of annealed Co₂P on Ti electrode is the best, which emphasizes the superiority of Co species in catalyzing HER reaction. Finally, the three magnetic metal phosphide catalysts are found to exhibit good stabilities in acidic conditions according to the galvanostatic testing results.     

Three-dimensional Ni2P–MoP2 mesoporous nanorods array as self-standing electrocatalyst for highly efficient hydrogen evolution

Electrochemical hydrogen evolution reaction (HER) via the splitting of water has required electrocatalysts with cost-effectiveness, environmentally friendliness, high catalytic activity, and superior stability to meet the hydrogen economy in future. In this context, we report the successful synthesis of self-standing mesoporous Ni₂P–MoP₂ nanorod arrays on nickel foam (Ni₂P–MoP₂ NRs/3D-NF) through an effective phosphidization of the corresponding NiMoO₄ NRs/3D-NF. The as-synthesis Ni₂P–MoP₂ NRs/3D-NF, as an efficient HER electrocatalyst, exhibits small overpotential of 82.2 and 124.7 mV to reach current density of 10 and 50 mA cm⁻², a low Tafel slope of 52.9 mV dec⁻¹ and it retains its catalytic performance for at least 20 h in alkaline condition. Our work also offers a new strategy in designing and using transition metal phosphide-based 3D nanoarrays catalysts with enhanced catalytic efficiency for mass production of hydrogen fuels.     

ZIF-67-derived nickel–cobalt phosphide nanocubes/N-doped carbon/nickel form composite for efficient overall water splitting

Hydrogen production from electrochemical water splitting is a promising strategy to generating green energy, which requires development of efficient and stable bifunctional catalysts for hydrogen and oxygen evolution reaction (HER/OER). Herein, dual transition metal phosphides/N-doped carbon/Nickel foam composite (CoNiP/NC-NF) is prepared via direct phosphidation of ZIF-67, in which ZIF-67 can control the size and N-doping content of CoNiP/NC, boosting the bifunctional activities for the OER and HER. Then, the overall water splitting is performed by using CoNiP/NC-NF as the cathode and anode, showing a low cell voltage of 1.60 V to reach current density of 10 mA cm⁻². Experimental studies indicate that ZIF-67 influences the electrocatalytic performance, and theoretical studies identify the active component of CoNiP/NC-NF for HER and OER, respectively.     

Synthesis of lawn-like NiS2 nanowires on carbon fiber paper as bifunctional electrode for water splitting

a low-cost electrode with lawn-like NiS₂ nanowire arrays on flexible carbon fiber paper was synthesized, for the first time, via sulfurization of Ni₂(CO₃)(OH)₂ precursor. And the performance of this electrode as a bifunctional electrocatalyst toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) was evaluated. It shows that NiS₂ NWs/CFP requires small overpotentials of 165 mV for HER and 246 mV for OER, respectively, to deliver the current density of 10 mA cm^?2 in 1.0 M KOH. The corresponding symmetric two-electrode alkaline water electrolyzer only needs a cell voltage of 1.59 V to afford 10 mA cm^?2 water-splitting current density.     

Highly efficient ternary CuP2/Ni1−xCux‒P@g-C3N4 nanostructure for improved hydrogen and oxygen evolution reactions

Herein, a highly active, and stable copper phosphide/nickel-copper phosphide (CuP₂/NiCuP) nanosheet supported by a g-C₃N₄ is constructed via phosphorization for hydrogen and oxygen evolution reactions (HER and OER, respectively). Strong coupling between CuP₂/NiCuP heteronanosheets and the structured g-C₃N₄ provides CuP₂/NiCuP/g-C₃N₄ with a regulated electronic state, sufficient anchored active sites, reduced mass transport distance, and improved structural stability. Consequently, the obtained CuP₂/(NiCu)_1:1P/g-C₃N₄ electrocatalyst manifests excellent performance in HER and OER, with overpotentials of 96 and 280 mV at 10 mA cm⁻², respectively, as well as stability. The excellent HER and OER activities are mainly ascribed to the collective effects of electronic structure engineering, strong interaction between CuP₂ and NiCuP in the heteronanojunction, abundant catalytic active sites, and highly conductive g-C₃N₄ support. This study provides novel insights for designing cost-effective bimetallic alloy-phosphide HER/OER electrocatalysts for various sustainable energy-conversion applications.     

Nickel nanocones as efficient and stable catalyst for electrochemical hydrogen evolution reaction

In this work, nickel nanocones (NNCs) were fabricated by single-step electrodeposition method. The NNCs were used as hydrogen evolution electrode and their electrocatalytic activity was compared with pure nickel film. Linear Sweep Voltammetry (LSV), Tafel polarization, Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and chronopotentiometry in 1 M KOH were used for study of the electrocatalytic activity for hydrogen evolution reaction (HER). The active surface area was increased by formation of NNCs and hence, the electrocatalytic activity of nickel electrode was improved. Results indicate that the current density corresponding to the amount of evolved hydrogen of NNCs is five times more than pure nickel film formed in the Watts bath.     

Efficient suppression of surface charge recombination by CoP-Modified nanoporous BiVO4 for photoelectrochemical water splitting

BiVO₄ is a promising photoanode material for water splitting due to its substantial absorption of solar light as well as favorable band edge positions. However, the poor water oxidation kinetics of BiVO₄ results in its insufficient photocurrent density. Herein, we demonstrate the use of CoP nanoparticles for facile surface modification of nanoporous BiVO₄ photoanode in potassium borate buffer solution (pH 9.0), which can generate a tremendous cathodic shift of ~430 mV in the onset potential for photoelectrochemical water oxidation. In addition, a remarkable photocurrent density of 4.1 mA cm^?2 is achieved at 1.23 V vs. RHE under AM 1.5G illumination. The photoelectrochemical measurement using sodium sulfite as a hole scavenger clearly shows that the greatly improved performances are attributed to the efficient suppression of interfacial charge recombination through loading of CoP catalyst. Moreover, the maximum surface charge injection yield can reach >81% at 1.23 V vs. RHE and the maximum IPCE of CoP/BiVO₄ can reach 75.8% at 420 nm, suggesting the potential application of CoP-modified BiVO₄ photoanode for overall solar water splitting in cost-effective tandem photoelectrochemical cells.     

Boosting performance of CdTe photocathode with pulse-reverse electrodeposited nickel telluride-nickel phosphide dual co-catalysts

Herein, noble-metal free Ni–Te/Ni–P dual co-catalysts are investigated as attractive candidates for improving the photoelectrochemical (PEC) performance of CdTe photocathodes. The Ni–Te/Ni–P dual co-catalysts are deposited on CdTe photocathodes via pulse-reverse electrodeposition and post annealing. The Ni–Te/Ni–P catalyzed CdTe photocathodes show a remarkable PEC performance, especially in terms of the photocurrent density, which is approximately 11.06 times higher than that of the pristine CdTe photocathode. The Ni–Te/Ni–P dual co-catalysts boost the catalytic activity via enhanced charge transfer and surface reaction kinetics. The photogenerated electrons and holes are effectively separated by the Schottky contact between the Ni–Te/Ni–P dual co-catalysts and the CdTe absorbing layer. Thus, the rational design of the CdTe photocathode with the Ni–Te/Ni–P dual co-catalysts can dramatically enhance the PEC performance of the CdTe photocathodes.     

An efficient way to improve water splitting electrocatalysis by electrodepositing cobalt phosphide nanosheets onto copper nanowires

Herein, catalysts with improved electrocatalysis of water splitting in alkaline media are accomplished by constructing bushy Cu nanowires on Cu foam to support cobalt phosphide nanosheets (Co–P/Cu NWs/CF). Results demonstrate that the highly efficient electroactivity of Co–P/Cu NWs/CF originates from the high intrinsic activity of Co–P species, Cu nanowires which possess accessible active sites, plentiful bubbles releasing channels, and honored electric conductivity, as well as the interaction between Cu NWs and Co–P species. To achieve a current density of 200 mA cm^?2, Co–P/Cu NWs/CF require an overpotential of only 155 mV for hydrogen evolution and 349 mV for oxygen evolution, which are less than that of Co–P/Cu(OH)₂ NWs/CF and Co–P/CF. This work provides a simple and efficient approach to designing water splitting electrocatalysts by manufacturing nanostructure-rich conductive substrates to support active species.     

In-situ grown of Ni2P nanoparticles on 2D black phosphorus as a novel hybrid catalyst for hydrogen evolution

Nickel phosphide-based nanomaterials have been acted as efficient catalysts for the hydrogen evolution reaction (HER), however, the design of novel and high performance HER catalyst is still a challenge. Herein, we report a novel 2D material black phosphorus (BP) as support for constructing Ni₂P-based hybrid catalyst by a one-pot thermal decomposition approach. TEM results indicated that the monodispersed Ni₂P nanoparticles with small size and good dispersion supported on the surface of layered BP, which implied that more catalytic active sites may be exposed for HER. The as-synthesized Ni₂P/BP hybrid exhibits high HER electrocatalytic performance with low onset overpotential (70 mV), small Tafel slope (81 mV dec^?1), large double-layer capacitance (1.24 mF cm^?2), high conductivity and good stability, which can be assigned to the strong synergistic effect between Ni₂P and BP. Therefore, BP may be a suitable support for constructing excellent catalysts in electrocatalysis.