Phase-dependent photo-assisted electrocatalytic conversion of nitrate to ammonia using TiO2: Insights into amorphous and rutile activity

The rise in nitrogen-containing compounds in water sources due to modern agricultural practices has intensified the need to effectively convert nitrate to ammonia, a valuable fertiliser and fuel. We developed a photo-assisted electrocatalytic system using a NiO/Au plasmon/TiO 2 composite to selectively reduce nitrate to ammonia under visible light, at neutral pH, and at room temperature. TiO 2 was found to be the active catalyst, but the precise active structure responsible for each catalytic step remains unclear, as the reaction involves a complex, multistep process. By analyzing the catalytic activity of different TiO 2 phases, we found that amorphous TiO 2 significantly enhances the nitrate-to-nitrite reduction step, increasing nitrite concentration in solution by nearly 50 % and resulting in a 10 % increase in Faradaic efficiency for this product. Conversely, the rutile phase plays a crucial role in the subsequent conversion of nitrite to ammonia. When the rutile phase was present, the ammonia yield more than doubled, leading to a 30 % increase in Faradaic efficiency. This phase-dependent behaviour provides critical insights into improving nitrate reduction efficiency, enabling sustainable agricultural practices that recycle nutrients, reduce fertiliser costs, and promote economic sustainability. • The role of the TiO 2 phase in nitrate reduction to ammonia. • Light activation boosts eco-friendly ammonia production. • Transformation of nitrates to ammonia benefits the environment and agriculture.