We must go beyond hydrogen, if we want safe and transportable fuels.
Hydrogen is energy-dense, but hard to compress, store, and transport. We research alternative fuels based on nitrogen, including ammonia (NH3), hydrazine (N2H4) and urea (CO(NH2)2). They are more easily liquefied and transported than hydrogen, and offer high energy density and/or high abundance.
However, storing energy in the nitrogen cycle (N2 ⇌ N-based fuel) is challenging; the nitrogen cycle is even harder to tame than the much investigated and still baffling hydrogen/oxygen cycle (H2O ⇌ H2 fuel). Featuring a broad range of oxidation states, and multiple stable intermediates, the nitrogen cycle is a rich and daunting challenge for electrocatalysis.
Some of the most promising catalysts in the nitrogen cycles are complex multi-doped carbons, whose very composition – not to mention catalytic site identification – is still uncertain. Materials such as Fe–N–C can oxidize hydrazine fuel and reduce N2 and NOx compounds. Thus, they are key to the development of sustainable and platinum-free electrocatalysts.
Our group investigates the complex structure and activity of such materials, in order to design new reactivity in the nitrogen cycle. Focusing on hydrazine, urea and ammonia fuels, we identify active sites, reaction mechanisms, and selectivity controls. These findings help us develop new, active and stable catalysts for direct nitrogen-fuel fuel cells.