Carbon Electrocatalysts for Hydrazine Oxidation: Self-Templating Design of Hierarchical Porosity Using Barium Carbonate Nanoparticles

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.