Valence-engineered MoNi4/MoOx@NF as a Bi-functional electrocatalyst compelling for urea-assisted water splitting reaction

Precise modulation of nickel-molybdenum alloy (MoNi4)/molybdenum dioxide nanowires via a ternary nickel-cobalt-iron complex for enhanced electrochemical overall water splitting

Developing renewable and clean energy technologies necessitates the design of efficient bifunctional catalysts that can facilitate electrochemical water splitting without relying on inert metals. This study presents a novel three-step strategy for fabricating nickel cobalt iron (NiCoFe)-modified nickel-molybdenum alloy/molybdenum dioxide (MoNi4/MoO2) nanowires on nickel foam (NF) substrates, denoted as NiCoFe-MoNi4/MoO2/NF. The synthesized catalyst demonstrates exceptional performance, achieving an impressively low overpotential (13 mV) at 10 mA·cm-2 current density for the hydrogen evolution reaction (HER) and 230 mV at 50 mA·cm-2 for the oxygen evolution reaction (OER). Its performance surpasses many noble-metal catalysts, achieving overall water splitting at just 1.51 V under 50 mA·cm-2. The distinctive one-dimensional (1D) nanostructure and synergistic interplay between the NiCoFe complex and the MoNi4/MoO2 framework enhance mass transfer, expose additional active sites, and enhance intrinsic activity, contributing to outstanding efficiency. Incorporating cobalt (Co) and iron (Fe) into the ternary complex greatly improved the efficiencies of both HER and OER, providing a promising approach for developing high-performance, cost-effective bifunctional electrocatalysts and promoting advancements in sustainable energy conversion technologies.

CeF3-Accelerated surface reconstruction of MoO2 nanosheets into coral-like CeF3/MoO2 composites enhances the oxygen evolution reaction for efficient water splitting

Developing efficient and cost-effective rare earth element-based electrocatalysts for water splitting remains a significant challenge. To address this, interface engineering and charge modulation strategies were employed to create a three-dimensional coral-like CeF3/MoO2 heterostructure electrocatalyst, grown in situ on the multistage porous channels of carbonized sugarcane fiber (CSF). Integrating abundant CeF3/MoO2 heterostructure interfaces and numerous oxygen vacancy defects significantly enhanced the catalyst's active sites and molecular activation capabilities. The prepared coral-like CeF3/MoO2/CSF catalyst achieves overpotentials as low as 29 mV and 210 mV for hydrogen evolution reaction and oxygen evolution reaction at 10 mA cm-2 current density, respectively. Notably, the CeF3/MoO2@CSF||CeF3/MoO2@CSF electrolyzer demonstrates a superior overall water splitting ability having a voltage of 1.53 V at 10 mA cm-2 and retains outstanding stability for 100 h operating in 1.0 M KOH electrolyte. The exceptional catalytic performance of CeF3/MoO2@CSF is attributed to the reduction in the water dissociation energy barrier, optimal adsorption/desorption behavior of H/O intermediates, and rapid mass transfer facilitated by the multistage porous channels. These findings, supported by experimental results and density functional theory (DFT) calculations, provide a novel approach for designing rare-earth metal heterojunctions and biomass-derived synergistic electrocatalysts for efficient water splitting.

Co2P-NiMoN/NF Heterostructure Nanorod Arrays as Efficient Bifunctional Electrocatalysts for Urea Electrolysis

Electrolysis of water represents an effective method for the generation of high-purity hydrogen. Nevertheless, the anodic oxygen evolution reaction (OER) exhibits slow kinetics, which leads to a high electrolytic potential and induces excessive energy consumption. In this work, nickel foam-supported 3D phosphide/bimetal nitride (Co2P-NiMoN/NF) nanorod array catalyst is prepared by calcination of NiMoO4, followed by phosphatization of Co(OH)2. The heterostructure catalyst exhibits excellent catalytic activity for cathodic hydrogen evolution reaction (HER: η100 = 98 mV, η1000 = 297 mV) and anodic OER (η100 = 277 mV, η1000 = 382 mV) of water electrolysis in alkaline electrolyte, indicating its feasibility as a bifunctional catalyst for overall water splitting (OWS). Additionally, at a current density of 100 mA cm-2, the associated oxidation potential is decreased by roughly 160 mV when the anodic OER is replaced with the urea oxidation process (UOR), which has a far lower thermodynamic equilibrium potential. Density functional theory (DFT) calculations reveal that the heterointerface between Co2P and NiMoN enriches the density of electronic states near the Fermi level, thereby enhancing electron transfer and promoting charge redistribution. This modulation precisely tunes the adsorption strengths of reactants during the reaction process, ultimately boosting the electrocatalytic performance. A current density of 100 mA cm-2 can be attained at a cell voltage of 1.51 V when Co2P-NiMoN/NF is used as the anode and cathode in the urea electrolysis cell. Notably, this cell potential is significantly lower compared to that of the water electrolysis cell (1.65 V), as well as the previously published values. The findings demonstrate that the Co2P-NiMoN/NF heterostructure can be used as a bifunctional catalyst for water and urea electrolysis and demonstrate an efficient strategy for the energy-efficient production of hydrogen through substituting UOR for OER at the anode of water electrolysis.

N, P co-doped Ni/Mo-based multicomponent electrocatalysts in situ decorated on Ni foam for overall water splitting

Developing the robust non-precious metal bifunctional electrocatalyst is highly imperative for the hydrogen evolution from overall water splitting. Herein, a Ni foam (NF)-supported ternary Ni/Mo bimetallic complex (Ni/Mo-TEC@NF), hierarchically constructed by coupling the in-situ formed MoNi₄ alloys and Ni₂Mo₃O₈ with Ni₃Mo₃C on NF, has been developed through a facile method involving the in-situ hydrothermal growth of the Ni-Mo oxides/polydopamine (NiMoO_x/PDA) complex on NF and a subsequent annealing in a reduction atmosphere. Synchronously, N and P atoms are co-doped into Ni/Mo-TEC during the annealing procedure using phosphomolybdic acid and PDA raw materials as P and N sources, respectively. The resultant N, P-Ni/Mo-TEC@NF shows outstanding electrocatalytic activities and tremendous stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), due to the multiple heterojunction effect-promoted electron transfer, the large number of exposed active sites, and the modulated electronic structure by the N and P co-doping. It only needs a low overpotential of 22 mV to afford the current density of 10 mA·cm^-2 for HER in alkaline electrolyte. More importantly, as the anode and cathode, it requires only 1.59 and 1.65 V to achieve 50 and 100 mA·cm^-2 for overall water splitting, respectively, comparable to the benchmark Pt/C@NF//RuO₂@NF couple. This work could spur the search for economical and efficient electrodes by in situ constructing multiple bimetallic components on 3D conductive substrates for practical hydrogen generation.

Efficient Self-Powered Overall Water Splitting by Ni4 Mo/MoO2 Heterogeneous Nanorods Trifunctional Electrocatalysts

The exploration of cost-effective multifunctional electrodes with high activity toward energy storage and conversion systems, such as self-powered alkaline water electrolysis, is very meaningful, although studies remain quite limited. Herein, a heterogeneous nickel-molybdenum (NiMo)-based electrode is fabricated for the first time as a trifunctional electrode for asymmetric supercapacitor (ASC), hydrogen evolution reaction, and oxygen evolution reaction. The trifunctional electrode consists of Ni₄ Mo and MoO₂ (denoted Ni₄ Mo/MoO₂ ) with hierarchical nanorod heterostructure and abundant heterogeneous nanointerfaces creating sufficient active sites and efficient charge transfer for achieving high performance self-power electrochemical devices. The ASC consists of the as-prepared Ni₄ Mo/MoO₂ positive electrode, showing a broad potential window of 1.6 V, and a maximum energy density of 115.6 Wh kg^-1 , while the alkaline overall water splitting (OWS) assembled using the as-prepared Ni₄ Mo/MoO₂ as bifunctional catalysts only requires a low cell voltage of 1.48 V to achieve a current density of 10 mA cm^-2 in aqueous alkaline electrolyte. Finally, by integrating the Ni₄ Mo/MoO₂ -based ASC and OWS devices, an aqueous self-powered OWS is assembled, which self-power the OWS to generate hydrogen gas and oxygen gas, verifying great potential of the as-prepared Ni₄ Mo/MoO₂ for sustainable and renewable energy storage and conversion system.