d-p-f orbital coupling for enhanced chlorine radical mediated ammonia-nitrogen wastewater purification.

During the chlorine evolution reaction, adsorbed chlorine radicals (Cl˙) at the anodic interface easily peroxidize to less reactive species, significantly inhibiting electrocatalytic chlorination performance. This study proposes a d-p-f orbital coupling strategy by introducing CeO x into spinel Cu x Co3-x O4 (CeO x /CuCoO) to optimize the CoOh 3+ electronic structure and suppress its reconfiguration for an enhanced chlorination process. Characterization and theoretical calculations confirm that the d-p-f orbital interaction of CoOh 3+-O-Ce4+ regulates CoOh 3+ from low spin (t6 2ge0 g) to intermediate spin (t5 2ge1 g). Electron transitions increase the eg orbital occupancy and lower the d-band center to balance the energy barriers of adsorption, activation, and desorption for Cl˙ generation. The required free energy for Cl˙ generation on CeO x /CuCoO is only 0.19 eV, lower than those of Cu x Co3-x O4 (0.50 eV) and Co3O4 (0.96 eV). The CeO x /CuCoO anode demonstrates feasibility in ammonia-nitrogen (NH4 +-N) chlorination treatment. The scale-up experiment using a continuous flow reactor realizes 100% of NH4 +-N and 89.1% of total nitrogen in landfill leachate continuously eliminated within 192 h, much superior to commercial dimensionally stable anodes. This work offers a new idea for the utilization of highly active species in electrocatalytic systems and guides the development of efficient chlorination electrodes.