Chromium phosphide nanoparticles embedded in porous nitrogen-/phosphorus-doped carbon as efficient electrocatalysts for a nitrogen reduction reaction

The resource recovery of heavy metals from effluent has significant environmental implications and potential commercial value. Chromium phosphide nanoparticles embedded in a nitrogen-/phosphorus-doped porous carbon matrix (CrP/NPC) are synthesized via a consecutive Cr⁶⁺ leachate treatment and resource recovery process. Electrochemical testing shows that CrP/NPC shows excellent nitrogen reduction reaction (NRR) performance, which yields the highest NH₃ production rate of 22.56 μg h⁻¹ mg⁻¹_cat. and Faradaic efficiency (16.37%) at −0.5 V versus the reversible hydrogen electrode in a 0.05 M Na₂SO₄ aqueous solution, as well as robust catalytic stability. The isotopic experiments using ¹⁵N₂ as a nitrogen source confirm that the detected NH₃ is derived from the NRR process. Finally, density functional theory (DFT) calculations show that the electron deficiency environment of the Cr site can significantly reduce the barrier of the NRR process and promote the formation of intermediate species.