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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/TiO2 composite to selectively reduce nitrate to ammonia under visible light, at neutral pH, and at room temperature. TiO2 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 TiO2 phases, we found that amorphous TiO2 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. |
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