Electrocatalytic dechlorination continually attracts attention in dealing with chlorinated volatile organic compounds (CVOCs) due to its mild reaction conditions, economical, and environmental friendliness. Unfortunately, the electrocatalysts were reported to suffer from low dechlorination reactivity and selectivity, as well as unclear active sites. Here, we developed a core−shell NiMn 2 O 4 (NiMn 2 O 4 −CS) via a facile solvothermal method as an efficient cathode catalyst for selective dechlorination of 1, 2-dichloroethane (1,2-DCA) into highly valuable ethylene. NiMn 2 O 4 −CS provided more active sites that could accelerate electron transfer efficiency and fix more intermediate species (*CH 2 CH 2 Cl). The as-prepared electrode showed significant current density (18.11 mA/cm 2 ) at a potential of −2.75 V (vs SCE) and an ethylene Faradaic efficiency of 41%. Transfer coefficient α points out a concerted mechanism of dechlorination. The first-principles calculations indicated that the Ni atoms in octahedral sites of NiMn 2 O 4 are the main active sites for 1,2-DCA dechlorination to ethylene. In addition, a remarkable charge transfer appeared between the intermediate of *CH 2 CH 2 Cl and the Ni oct sites of NiMn 2 O 4 . This work provides reasonable ideas for the design of dechlorination electrocatalysts and the friendly transformation of CVOCs.

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CuFe 2 O 4 spinel has been considered as a promising catalyst for the electrochemical reaction, while the nature of the crystal phase on its intrinsic activity and the kind of active site need to be further explored. Herein, the crystal phase-dependent catalytic behavior and the main active sites of CuFe 2 O 4 spinel for electrochemical dechlorination of 1,2-dichloroethane are carefully studied based on the combination of experiments and theoretical calculations. Cubic and tetragonal CuFe 2 O 4 are successfully prepared by a facile sol−gel method combined with high temperature calcination. Impressively, CuFe 2 O 4 with the cubic phase shows a higher activity and ethylene selectivity compared to CuFe 2 O 4 with the tetragonal phase, suggesting a significant facilitation of electrocatalytic performance by the cubic crystal structure. Moreover, the octahedral Fe atom on the surface of cubic CuFe 2 O 4 (311) is the active site responsible to produce ethylene with the energy barrier of 0.40 eV. This work demonstrates the significance of crystal phase engineering for the optimization of electrocatalytic performance and offers an efficient strategy for the development of advanced electrocatalysts.

Cobaltate MCo 2 O 4−δ (M = Zn, Ni, Cu) spinel composites have been known as promising catalysts for the manufacture of fuels and fine chemicals by CO 2 photocatalytic fixing reaction (CO 2 PFR), whereas CO 2 PFR product selectivity based on different cobaltate remains poorly understood. Herein, various cobaltate spinel composites with different cations distribution hierarchical nanomicrospheres (HNMs) were rationally designed and synthesized. We found that among the cobaltate MCo 2 O 4−δ (M = Zn, Ni, Cu) spinel catalysts, CuCo 2 O 4−δ DSHoMs show the most substantially promoted CO production rate (26.54 μmol h −1 ), while the CH 4 yields of NiCo 2 O 4−δ SMs were ≈1.7 times higher than that of CuCo 2 O 4−δ DSHoMs. As collectively evidenced by PEC, in situ DRIFTS, TPD, and theoretical results, NiCo 2 O 4−δ SMs feature promotional charge transferability and super CH 4 selectivity, while CuCo 2 O 4−δ DSHoMs feature higher light adsorption, high transient photocurrent density, and preferential selectivity of CH 4 evolution. This work unearths atomic-level insights into the correlation between the distribution of metal cations in cobalt-based spinel structures and selectivity regulation for CO 2 PFR and deeper understanding of the intrinsic relationship of metal species property between various cobaltate spinel oxides which lays a firm foundation for controlling and tailoring of the selectivity of the desired products during CO 2 PFR.