Mo propellant boosting the activity of Ni-P for efficient urea-assisted water electrolysis of hydrogen evolution

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.

Electronic Structure Modulation Via Iron-Incorporated NiO to Boost Urea Oxidation/Oxygen Evolution Reaction

The urea-assisted water splitting not only enables a reduction in energy consumption during hydrogen production but also addresses the issue of environmental pollution caused by urea. Doping heterogeneous atoms in Ni-based electrocatalysts is considered an efficient means for regulating the electronic structure of Ni sites in catalytic processes. However, the current methodologies for synthesizing heteroatom-doped Ni-based electrocatalysts exhibit certain limitations, including intricate experimental procedures, prolonged reaction durations, and low product yield. Herein, Fe-doped NiO electrocatalysts were successfully synthesized using a rapid and facile solution combustion method, enabling the synthesis of 1.1107 g within a mere 5 min. The incorporation of iron atoms facilitates the modulation of the electronic environment around Ni atoms, generating a substantial decrease in the Gibbs free energy of intermediate species for the Fe-NiO catalyst. This modification promotes efficient cleavage of C-N bonds and consequently enhances the catalytic performance of UOR. Benefiting from the tunability of the electronic environment around the active sites and its efficient electron transfer, Fe-NiO electrocatalysts only needs 1.334 V to achieve 50 mA cm-2 during UOR. Moreover, Fe-NiO catalysts were integrated into a dual electrode urea electrolytic system, requiring only 1.43 V of cell voltage at 10 mA cm-2.

Amorphous Fe-Co oxide as an active and durable bifunctional catalyst for the urea-assisted H2 evolution reaction in seawater

In this study, we prepared amorphous iron-cobalt oxide through the dealloying of trimetallic FeCoAl, showing excellent performance in both urea oxidation and hydrogen evolution reactions (UOR and HER) in alkaline seawater. The catalyst demonstrated stable UOR and HER activity during long-term operations due to the abundant active sites and oxygen vacancies. The catalyst required applied potentials of 1.52 and -0.185 V to yield 100 mA cm-2 for the UOR and HER, respectively. Moreover, when used as both the cathode and anode, the electrolyzer required a working voltage of 1.68 V to yield 100 mA cm-2 for urea-assisted hydrogen production.

Heterogeneous Ni-MoN nanosheet-assembled microspheres for urea-assisted hydrogen production

Electrocatalytic water splitting is a promising technology for sustainable hydrogen (H₂) production; however, it is restricted by the kinetically sluggish anodic oxygen evolution reaction (OER). Replacing OER with urea oxidation reaction (UOR) with low thermodynamic potential can simultaneously improve the energy efficiency of H₂ production and purify urea-containing wastewater. Here we report a facile assembly-calcination two-step method to synthesize heterogeneous Ni-MoN nanosheet-assembled microspheres (Ni-MoN NAMs). The nanosheet-assembled structure and the synergistic metallic Ni-MoN heterogeneous interface endow the Ni-MoN NAMs with good OER (1.52 V@10 mA cm^-2), UOR (1.28 V@10 mA cm^-2), and hydrogen evolution reaction (HER, 0.16 V@10 mA cm^-2) activity. The two-electrode urea electrolysis cell with Ni-MoN NAMs as both the cathode and anode requires an extremely low cell voltage of 1.41 V to afford 20 mA cm^-2, which is 0.3 V lower than that of the water electrolyzer, paving the way for energy-saving H₂ production.

P-induced bottom-up growth of Fe-doped Ni12P5 nanorod arrays for urea oxidation reaction

Synthesis of regular morphology catalysts with self-growing substrates is one of the effective methods to solve the problem of easy shedding of heterogeneous catalysts. In this study, Fe-doped Ni₁₂P₅ nanorods were prepared by depositing 1,1' -bis (diphenylphosphine) ferrocene (DPPF) on N-doped C/NF. The bottom-up growth of the nanorod is ascribed to the preferential adsorption of DPPF with a P site to NF that is surface-doped with the solid-solving C, and the length of nanorods can reach tens of microns and has good robustness. The N-doped carbon-constrained rod-shaped Fe-doped Ni₁₂P₅ catalyst (Fe-Ni₁₂P₅/N_dC/NF-800) that grows on NF has excellent catalytic performance for the urea oxidation reaction. In addition, the current density can be maintained as high as 100 mA cm^-2 and the current attenuation is weak for 12 h, and the rod shape remains good. This work provides a new idea for synthesizing self-growing catalysts with regular morphology to improve the performance of heterogeneous catalysts.