Flower-like Co nano-particles deposited on Ni foam substrate as efficient noble metal-free catalyst for hydrazine oxidation

Crystalline Cobalt/Amorphous LaCoOx Hybrid Nanoparticles Embedded in Porous Nitrogen-Doped Carbon as Efficient Electrocatalysts for Hydrazine-Assisted Hydrogen Production

Hydrazine electro-oxidation has received substantial attention owing to its high energy density, low onset potential, and wide applications in hydrazine-assisted hydrogen production and direct hydrazine fuel cells. In this work, crystalline cobalt/amorphous LaCoO_x hybrid nanoparticles embedded in porous nitrogen-doped carbon (N-C) were fabricated via pyrolytic decomposition of the dual-metal lanthanum-incorporated zeolitic imidazolate framework (La/ZIF-67), which exhibit high activity and stability toward the electrocatalytic hydrazine oxidation reaction (HzOR). The hybrid nanoparticles based on metallic cobalt and amorphous LaCoO_x could provide abundant active sites for HzOR catalysis, while the highly conductive and porous N-C could act as both robust skeleton for anchoring the active hybrid nanoparticles and facile charge transport pathway for the HzOR process, thereby resulting in enhanced HzOR activity. With the synergistic merits of enriched active sites, a large surface area, enhanced charge-transfer ability, and intimate catalyst anchoring, promoted HzOR performance with high activity and stability was achieved for the optimized catalyst, which shows an ultralow onset potential of -0.17 V versus reversible hydrogen electrode (RHE), high HzOR current density of 69.2 mA cm^-2 at 0.3 V versus RHE, and superior stability for 20 h continuous catalysis, making the catalyst a promising electrode material for hydrazine-assisted hydrogen production.

CoPtx/γ-Al2O3 bimetallic nanoalloys as promising catalysts for hydrazine electrooxidation

Stable bimetallic catalysts composed of CoPtx/γ-Al2O3 (x = Pt/Co molar ratio) were synthesized by wet impregnation method followed by calcination and the H2 reduction. The powders were characterized using XRD, AAS, BET, SEM, EDX, TPR, and TPO techniques. The prepared catalysts were drop casted on the glassy carbon electrode (GCE) and catalytic performance was examined for hydrazine electrooxidation in alkaline medium via cyclic voltammetry (CV). All the compositions in CoPtx/γ-Al2O3 series showed high responses towards hydrazine electrooxidation, however; high activity of CoPt0.034/γ-Al2O3 catalyst inferred it as a best material with an anodic peak current (iP) response of 200 μA at 0.86 V. The prominent electrochemical (EC) responses for this composition are attributed to better accessible surface area resulting in a fast electron transfer. The CoPtx/γ-Al2O3 catalysts are reported as the robust and superior prospective materials for extensive electroanalytical and catalytic studies.

Heteroatom-Doped Carbon Materials for Hydrazine Oxidation

The key in designing efficient direct liquid fuel cells (DLFCs), which can offer some solutions to society's grand challenges associated with sustainability and energy future, currently lies in the development of cost-effective electrocatalysts. Among the many types of fuel cells, direct hydrazine fuel cells (DHFCs) are of particular interest, especially due to their high theoretical cell voltages and clean emission. However, DHFCs currently use noble-metal-based electrocatalysts, and the scarcity and high cost of noble metals are hindering these fuel cells from finding large-scale practical applications. In order to replace noble-metal-based electrocatalysts with sustainable ones and help DHFCs become widely usable, great efforts are being made to develop stable heteroatom (e.g., B, N, O, P and S)-doped carbon electrocatalysts, the activities of which are comparable to, or better than, those of noble metals. Here, the recent research progress and the advancements made on the development of heteroatom-doped carbon materials, their general properties, their electrocatalytic activities toward the HzOR, and their dopant- and structure-related electrocatalytic properties for the HzOR are summarized. Perspectives on the different directions that the research endeavors in this field need to take in the future and the challenges associated with DHFCs are included.

In situ grown Ni phosphide nanowire array on Ni foam as a high-performance catalyst for hydrazine electrooxidation

Synthesis of high-performance and cost-effective electrocatalysts towards hydrazine electrooxidation is vital to develop the direct hydrazine fuel cell (DHFC) as a viable energy conversion technology. Herein, we report a combined experimental and theoretical study of nickel phosphides (NixP) as promising catalysts for hydrazine electrooxidation. NixP nanowire array supported on a Ni foam (NF) was synthesized by a one-step phosphorization method using hypophosphite as a P-source. Ni12P5 and Ni2P phases are observed as the products of the direct phosphorization of commercial NF under the applied conditions with Ni2P nanoparticles exclusively distributing on the surface of Ni12P5. The NixP/NF catalyst exhibits a synergetic capabilities of exceptionally high activity, excellent durability and nearly 100% selectivity towards the complete electrooxidation of hydrazine in alkaline condition, which is among the best performance reported on hydrazine electrooxidation catalysts. First-principles calculations have been conducted to gain insight into the catalytic mechanism of Ni phosphides towards hydrazine electrooxidation.