We report an efficient electrocatalyst for the oxidation of hydrazine,apromising fuel for fuel cells and an important analyte for health and environmental monitoring. To design this material, we emulated natural nitrogen-cycle enzymes,f ocusing on designing ac ooperative,m ulti-doped active site.T he catalytic oxidation occurs on Fe 2 MoC nanoparticles and on edge-positioned nitrogen dopants,a ll welldispersed on ah ierarchically porous,g raphitic carbon matrix that provides active site exposure to mass-transfer and charge flow. The new catalyst is the first carbide with HzOR activity.It operates at the most negative onset potentials reported for carbon-based HzOR catalysts at pH 14 (0.28 Vvs. RHE), and has good-to-excellent activity at pH values down to 0. It shows high faradaic efficiency for oxidation to N 2 (3.6 e À /N 2 H 4 ), and is perfectly stable for at least 2000 cycles. Conflict of interestTheauthors declare no conflict of interest.

Fe–N–C electrocatalysts hold a great promise for Pt-free energy conversion, driving the electrocatalysis of oxygen reduction and evolution, oxidation of nitrogen fuels, and reduction of N2, CO2, and NOx. Nevertheless,...

To enable hydrazine as a clean fuel in next-generation fuel cells, electrocatalysts are sought for the hydrazine oxidation reaction (HzOR). Nanostructure of the electrocatalyst plays a crucial role in electrocatalytic activity, yet rational design of surface area, hierarchical porosity, doping and conductivity is highly challenging. We now report a systematic investigation into the structural evolution of excellent HzOR electrocatalysts. This hierarchically porous, N-doped carbon was derived by the tunable self-templating strategy from a simple, well-defined metal-organic coordination polymer (barium nitrilotriacetate). To understand the evolution of structure and its effect on electrocatalytic activity, we combined XRD, HRSEM, TEM, XPS, Raman spectroscopy, elemental analysis, N2 porosimetry, and voltammetry. The sizes, shapes and distributions of BaCO3 nanoparticles and agglomerates were found to be temperature-dependent, and strongly correlated to the hierarchical porosity in the ultimate carbons. The final carbons display a multi-modal porosity, high surface areas (up to 1030 m2 g−1), high nitrogen content (up to 2.7 at%), and excellent graphitization. The best catalysts, prepared at 700 °C and 800 °C, begin electro-oxidizing hydrazine at onset potentials as low as 0.34 V vs RHE at pH 14—within a few 10 s mVs of the best metal-free HzOR electrocatalysts ever reported.

Hierarchical porosity in carbon materials can be realized by self-templating: controlled pyrolysis of well-designed metal–organic precursors.

The urea oxidation reaction (UOR) is an important challenge in electrocatalysis, in the context of electrolyzers, fuel cells, medical sensing, and bio-waste treatment. The leading electrocatalysts for the UOR are nickel hydroxide surfaces, operating by the Botte mechanism: Ni II (OH) 2 is oxidized to Ni III OOH, and the latter drives the UOR. However, these materials have several polymorphs, with αand β-Ni(OH) 2 , and γand β-NiOOH, as described by the Bode diagram. We now report a systematic study of a series of nickel hydroxides, varying gradually from α-rich to β-rich materials. The crystallinity, order, hydration, intercalation, and morphology of these materials have been characterized by XRD, Raman, ATR-FTIR, XPS, and HRSEM and linked to their electrochemical activity. The disordered α phase was found to be superior to the β phase as a UOR electrocatalyst, with an oxidation onset potential of 0.31 V vs. SCE, better reversibility, and higher anodic current densities. Moreover, the perfect match in onset potentials between UOR electrocatalysis and the Ni 2+ /Ni 3+ oxidation was observed for both phases, suggesting that the Botte mechanism is true for both the α-Ni(OH) 2 /γ-NiOOH couple and the β-Ni(OH) 2 /β-NiOOH couple. We further characterize the dynamic behavior of these materials (activation and aging), allowing us to propose a unified Botte-Bode diagram of UOR on Ni(OH) 2 /NiOOH.