Modulation of the electronic structure of CoP active sites by Er-doping for nitrite reduction for ammonia electrosynthesis

doi:10.1016/S1872-2067(24)60224-X

Abstract

Abstract:

The electrochemical conversion of toxic nitrite (NO₂^-) is a promising approach for the simultaneous removal of nitrogen contaminants and synthesis of ammonia (NH₃). In this study, we present the Er-doping-induced electronic modulation of CoP integrated with nitrogen-doped carbon (CN) nanosheets supported on a titanium mesh (Er-CoP@NC/TM) for the electrocatalytic NO₂^- reduction reaction (eNO₂^-RR) for NH₃ synthesis. The catalyst demonstrates a high Faraday efficiency of 97.08 ± 2.22% and a high yield of 2087.60 ± 17.10 µmol h^-1 cm^-2 for NH₃ production. Characterization and theoretical calculations revealed that Er-doping facilitated the electronic modulation of CoP in Er-CoP@NC/TM, which regulated the adsorption behaviors of intermediates and was the rate-limiting step for the eNO₂^-RR, thereby enhancing the electrocatalytic performance. Quenching experiments and electron paramagnetic resonance tests suggest that both direct electrocatalytic reduction by active hydrogen and electron transfer are critical for the eNO₂^-RR for NH₃ synthesis. Furthermore, Er-CoP@NC/TM exhibited high performance across a wide range of NO₂^- concentrations (0.05-0.1 mol L^-1) and pH values (4-13). In addition, the catalyst demonstrated strong resistance to anions and a long cycle life in simulated wastewater environments. This study offers a powerful approach for the remediation of NO₂^- wastewater and recovery of valuable inorganic compounds.

Key words: Electrocatalysis, Nitrite reduction, Ammonia production, Cobalt phosphide, Er-doping

Donglin Zhao, Keyu Zhou, Li Zhan, Guangyin Fan, Yan Long, Shuyan Song. Modulation of the electronic structure of CoP active sites by Er-doping for nitrite reduction for ammonia electrosynthesis[J]. Chinese Journal of Catalysis, 2025, 70: 299-310.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(24)60224-X

https://www.cjcatal.com/EN/Y2025/V70/I3/299

Figures/Tables 8

Fig. 1. (a) Detailed illustration of the fabrication process of Er-CoP@NC/TM. Low (b) and high (c) magnification SEM images, TEM image (insets are particle size distributions) (d), HRTEM image (e), SAED (f), and elemental mappings (g,h) of Er-CoP@NC/TM.

Fig. 2. (a) XRD patterns of CoP@NC/TM and Er-CoP@NC/TM. High resolution XPS spectra of Er 4d (b), Co 2p (c), P 2p (d), C 1s (e), and N 1s (f) for CoP@NC/TM and Er-CoP@NC/TM.

Fig. 3. (a) LSV curves of CoP@NC/TM and Er-CoP@NC/TM in 0.1 mol L-1 KOH with and without 0.1 mol L-1 NO2-. (b) Influences of operating voltages on NH3 yields and FEs in alkaline conditions. (c) NH3 yields and FEs of various electrodes at -0.4 V. (d) NH3 yields and FEs of Er-CoP@NC/TM and previously developed catalysts. (e) FEs of NH3, N2, and H2 of Er-CoP@NC/TM at different electrode potentials. (f) Effects of NO2- concentrations on NH3 yields and FEs with Er-CoP@NC/TM. (g) NH3 yields under various conditions. (h) Electrocatalytic performance of Er-CoP@NC/TM under alternative cycle tests. (i) 1H NMR spectra (600 MHz) of the electrolyte after eNO2-RR at -0.4 V.

Fig. 4. Chronoamperometry curves (a) and cycling performance (b) of Er-CoP@NC/TM for eNO2-RR at -0.4 V. Conversion of NO2- versus electrolysis time (c) and the corresponding FEs and NH3 concentrations (d).

Fig. 5. LSV curves of Er-CoP@NC/TM in 0.1 mol L-1 PBS (a) and in 0.05 mol L-1 H2SO4/0.1 mol L-1 K2SO4 (b) with and without 0.1 mol L-1 NO2-. The NH3 yields and FEs of Er-CoP@NC/TM in neutral (c) and acidic media (d) at different operating voltages.

Fig. 6. (a) NH3 yields and FEs of Er-CoP@NC/TM in NO2- solutions containing different electrolytes. (b) Chronoamperometry curves of Er-CoP@NC/TM during cycling tests at -0.4 V. (c) NH3 yields and FEs of Er-CoP@NC/TM in solutions containing different electrolytes.

Fig. 7. (a) LSV curves with or without tertiary butanol (TBA). (b) EPR spectra of solutions (with or without nitrite) with different c(NO2-) using DMPO as the radical trapping reagent of Er-CoP@NC/TM. (c) NH3 yield rates with and without 0.5 mol L-1 TBA. (d,e) Electrochemical in situ Raman spectra of Er-CoP@NC/TM. (f) Electrochemical in situ FTIR on the Er-CoP@NC/TM electrode in 0.1 mol L-1 KOH containing 0.1 mol L-1 NO2-.

Fig. 8. (a) Difference between the charge densities of CoP@NC/TM and Er-CoP@NC/TM, with purple indicating electron enrichment and blue indicating electron deficiency. (b) Free energy diagram for the NO2-RR on CoP@NC/TM and Er-CoP@NC/TM without applied potential at pH = 13 and T = 298 K. (c) Free energy diagram for the HER on different active metal sites of CoP@NC/TM and Er-CoP@NC/TM without applied potential at pH = 0 and T = 298 K.

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