Recently, Prof Jia’s group proposed an efficient and effective screening strategy towards trifunctional catalysts for the simultaneous electroreduction of NO₃⁻, NO₂⁻ and NO to NH₃, and the work was published on Journal of Materials Chemistry A. The paper can be obtained from https://pubs.rsc.org/en/content/articlelanding/2022/TA/D2TA00192F.

Figure. Based on the key protonation process, the screening flow to search the trifunctional electrocatalyst that can simultaneously reduce the NO₃⁻, NO₂⁻ and NO to produce NH₃.

The electrocatalytic reductions of NO₃⁻ (NO₃RR), NO₂⁻ (NO₂RR) and NO (NORR) are attracting extensive attentions, which can not only produce NH₃ under ambient condition beyond NRR and Haber-Bosch process, but also remove the waste NO_x species. It should be noted that nitrate and nitrite ions usually coexist in the waste-water, such as the contaminated groundwater, lakes, and coastal water, which also includes NO from biological denitrification. To this end, developing trifunctional electrocatalysts that simultaneously reduce all the NO_x species promises higher conversion efficiency for NH₃ synthesis compared with the monofunctional ones.

The NORR is an essential reaction for determining the performance of electrocatalysts for NO₃⁻and NO₂⁻ to NH₃. By using the first-principles method, this work proposed an efficient strategy to screen NO_xRR multifunctional electrocatalysts, which focuses on the key protonation process of the essential NORR for NO_xRR (see the Figure). Taking double-atom catalysts (DAC) with transition-metal dimers (M1/M2 = V, Cr, Mn, Fe, Co, Ni, and Cu) embedded N-doped graphene as examples, it showed that the proposed strategy was effective for electrocatalyst screening, and it identified the Cu₂@NG to be the best one. A simple descriptor for evaluating electrocatalytic activity was established, i.e., the total number of metal-dimer d-orbital valence electrons. Based on this descriptor, for the screening test in some 4d and 5d late transition-metal based DACs, the proposed strategy was confirmed to be feasible and efficient to find another NO_xRR multifunctional electrocatalyst.

Recently, some bifunctional (NO₂RR and NO₃RR) electrocatalysts with high catalytic activity have been found experimentally, such as Rux@POC [CCS Chem., DOI: 10.31635/ccschem. 022.202101756 (2022)], and the trifunctional (NORR, NO₂RR and NO₃RR) CuFe-CP electrocatalyst [Chem Catal., 2, 622 (2022)]. In addition, the proposed strategy for screening trifunctional NO_xRR electrocatalyst saves time and effort by eliminating the works to calculate the Gibbs free energy of all reaction steps. Therefore, this work has important theoretical guiding significance and potential scientific application value.

The first author of this paper is Dr. Peng Lv of Key Laboratory of Special Functional Materials, and the corresponding authors are professor Dongwei Ma and Yu Jia. This work is supported by the National Natural Science Foundation of China and the Key Scientific Research Foundation for universities of Henan Province.