Hydrogen spillover for boosted catalytic activity towards hydrazine oxidation

A nanoflower-like MoO2-Rh electrocatalyst exhibits a 3.5-fold higher mass activity in the hydrazine oxidation reaction compared with metallic Rh, attributed to the hydrogen spillover, acting as a hydrogen pump to deplete hydrogen from the Rh active site.

Alumina supported copper oxide nanoparticles (CuO/Al2O3) as high-performance electrocatalysts for hydrazine oxidation reaction

Direct hydrazine liquid fuel cell (DHFC) is perceived as effectual energy generating mean owing to high conversion efficiency and energy density. However, the development of well-designed, cost effective and high performance electrocatalysts is the paramount to establish DHFCs as efficient energy generating technology. Herein, gamma alumina supported copper oxide nanocatalysts (CuO/Al₂O₃) are synthesized via impregnation method and investigated for their electrocatalytic potential towards hydrazine oxidation reaction. CuO with different weight percentages i.e., 4%, 8%, 12%, 16% and 20% are impregnated on gamma alumina support. X-ray diffraction analysis revealed the cubic crystal structure and nanosized particles of the prepared metal oxides. Transmission electron microscopy also referred to the cubic morphology and nanoparticle formation. Electrochemical oxidation potential of the CuO/Al₂O₃ nanoparticles is explored via cyclic voltammetry as the analytical tool. Optimization of conditions and electrocatalytic studies shown that 16% CuO/Al₂O₃ presented the best electronic properties towards N₂H₂ oxidation reaction. BET analysis ascertained the high surface area (131.2546 m² g¹) and large pore diameter (0.279605 cm³ g^-1) for 16% CuO/Al₂O₃. Nanoparticle formation, high porosity and enlarged surface area of the proposed catalysts resulted in significant oxidation current output (600 μA), high current density (8.2 mA cm^-2) and low charge transfer resistance (3.7 kΩ). Electrooxidation of hydrazine on such an affordable and novel electrocatalyst opens a gateway to further explore the metal oxide impregnated alumina materials for different electrochemical applications.

Ligand-Tuned Energetics for the Selective Synthesis of Ni2P and Ni12P5 Possessing Bifunctional Electrocatalytic Activity toward Hydrogen Evolution and Hydrazine Oxidation Reactions

The occurrence of many phases and stoichiometries of nickel phosphides calls for the development of synthetic levers to selectively produce phases with purity. Herein, thiol (-SH) and carboxylate (-COO^-) functional groups in ligands were found to effectively tune the energetics of nickel phosphide phases during hydrothermal synthesis. The initial kinetic product Ni₂P transforms into thermodynamically stable Ni₁₂P₅ at longer reaction times. The binding of carboxylate onto Ni₂P promotes this phase transformation to produce pure-phase Ni₁₂P₅ within 5 h compared to previous reports (∼48 h). Thiol-containing ligands inhibit this transformation process by providing higher stability to the Ni₂P phase. Cysteine-capped Ni₂P showed excellent geometric and intrinsic electrocatalytic activity toward both hydrogen evolution and hydrazine oxidation reactions under alkaline conditions. This bifunctional electrocatalytic nature enables cysteine-capped Ni₂P to promote hydrazine-assisted hydrogen generation that requires lower energy (0.46 V to achieve 10 mA/cm_geo²) compared to the conventional overall water splitting (1.81 V to achieve 10 mA/cm_geo²) for hydrogen generation.

Trace Amount of NiP2 Cooperative CoMoP Nanosheets Inducing Efficient Hydrogen Evolution

As a very attractive clean energy, hydrogen has a high energy density and great potential to achieve zero pollution emission. Therefore, the preparation of hydrogen evolution electrocatalysts with excellent performance is an urgent task to ameliorate the global energy shortage and environmental pollution. Here, a trace amount of NiP₂ coupled with CoMoP nanosheets (NCMP) was synthesized by the one-step hydrothermal method and low-temperature phosphidation. Studies have found that although the dosage of NiP₂ is very low, its appearance has been efficient to improve the hydrogen evolution reaction (HER) performance of CoMoP, which may be induced by the synergistic effect of the two different components NiP₂ and CoMoP. To find the superior catalyst, the effect of Ni content on the catalyst performance is also studied, and it is found that when the dosage of Ni is 0.02 mM, NCMP-2 (2 means 0.02 mM) displays the most outstanding overpotential (10 mA cm^-2) of 46 mV.

Ultrathin NiSe Nanosheets on Ni Foam for Efficient and Durable Hydrazine-Assisted Electrolytic Hydrogen Production

Hydrazine-assisted electrochemical water splitting is an important avenue toward low cost and sustainable hydrogen production. An efficient and stable bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and the anodic hydrazine oxidation reaction (HzOR) is fundamental to this goal. Herein, we employed a facile method to fabricate ultrathin NiSe nanosheet arrays on nickel foam (NiSe/NF), which exhibits predominant electrocatalytic activity for both HER and HzOR. Our investigations revealed that the excellent electrocatalytic activity of the NiSe/NF mainly arises from the abundant electrocatalytic active sites endowed by the ultrathin nanosheet morphology, the rugged feature of the extended (100) nanosheet surface, the rich presence of Se on the nanosheet surface, and the three-dimensional (3D) porous structure of the NF and other factors such as high conductivity of the NiSe/NF and strong NiSe-NF adhesion. We assembled a hydrazine-boosted electrochemical water splitting cell using NiSe/NF as a bifunctional catalyst for both of the electrodes, and the constructed cell exhibits an ultralow overpotential (310 mV at 10 mA cm^-2), which is robust for 30 h continuous electrolysis in a 1 M KOH electrolyte. This work provides a promising avenue toward low cost, high-efficiency, and stable hydrogen production based on hydrazine-assisted electrolytic water splitting for future.

Interfacial engineering of Mo2C-Mo3C2 heteronanowires for high performance hydrogen evolution reactions

Non-precious metal-based electrocatalysts with high activity and stability for efficient hydrogen evolution reactions are of critical importance for low-cost and large-scale water splitting. In this work, Mo₂C-Mo₃C₂ heteronanowires with significantly enhanced catalytic performance are constructed from an MoAn precursor via an accurate phase transition process. The structure disordering and surface carbon shell of Mo₂C-Mo₃C₂ heteronanowires can be precisely regulated, resulting in an enlarged surface area and a defect-rich catalytic surface. Density functional theory calculations are used to identify the effect of the defective sites and carbon shell on the free energy for hydrogen adsorption in hydrogen evolution. Meanwhile, the synergistic effect between different phases and the introduced lattice defects of Mo₂C-Mo₃C₂ are considered to enhance the HER catalytic performance. The designed catalyst exhibits optimal electrocatalytic activity in both acidic and alkaline media: low overpotentials of 134 and 116 mV at 10 mA cm^-2, a small Tafel slope of 64 mV dec^-1, and a long-term stability for 5000 cycles. This work will provide new insights into the design of high-efficiency HER catalysts via interfacial engineering at the nanoscale for commercial water splitting.