In Situ Reconstruction of Metal Oxide Cathodes for Ammonium Generation from High-Strength Nitrate Wastewater: Elucidating the Role of the Substrate in the Performance of Co₃O_4-x

Abstract

In situ electrochemical reconstruction is important for transition metal oxides explored as electrocatalysts for electrochemical nitrate reduction reactions (ENRRs). Herein, we report substantial performance enhancement of ammonium generation on Co, Fe, Ni, Cu, Ti, and W oxide-based cathodes upon reconstruction. Among them, the performance of a freestanding ER-Co 3 O 4-x /CF (Co 3 O 4 grown on Co foil subjected to electrochemical reduction) cathode was superior to its unreconstructed counterpart and other cathodes; e.g., an ammonium yield of 0.46 mmol h −1 cm −2 , an ammonium selectivity of 100%, and a Faradaic efficiency of 99.9% were attained at −1.3 V in a 1400 mg L −1 NO 3 − −N solution. The reconstruction behaviors were found to vary with the underlying substrate. The inert carbon cloth only acted as a supporting matrix for immobilizing Co 3 O 4 , without appreciable electronic interactions between them. A combination of physicochemical characterizations and theoretical modeling provided compelling evidence that the CF-promoted self-reconstruction of Co 3 O 4 induced the evolution of metallic Co and the creation of oxygen vacancies, which promoted and optimized interfacial nitrate adsorption and water dissociation, thus boosting the ENRR performance. The ER-Co 3 O 4-x /CF cathode performed well over wide ranges of pH and applied current and at high nitrate loadings, ensuring its high efficacy in treating high-strength real wastewater.

Unveiling the Critical Role of Surface Hydroxyl Groups for Electro-Assisted Uranium Extraction from Wastewater

“…Compared to the referenced Co foil and Co 3 O 4 , the XANES characters of CoO x were distinctly different from those of the Co foil and Co 3 O 4 , indicating the unique local structure of Co. Considering that the white line peak of the Co K-edge arose from the transition between the 1s and 3d orbitals, the Co K-edge of CoO x catalysts presented a similar energy absorption with the Co 3 O 4 reference, suggesting the valence states of Co atoms in CoO x catalysts were predominantly +2 and +3, in good agreement with the Co 2p XPS results (Figure2g) 37.…”

Recent Progress and Perspectives on Transition Metal-Based Electrocatalysts for Efficient Nitrate Reduction

“…Liu et al 23 used Rh nanoflowers (Rh NFs) assembled from ultrathin nanosheets (with a diameter of 200 nm) for electrochemical nitrate reduction (the SEM and TEM images are shown in Figure 3a,b). The lattice spacing of Rh NFs is 0.22 nm, as shown in the HRTEM image in Figure 3c, which corresponds to the Rh (111) plane. Under the optimal potential of 0.2 V vs RHE, the Faraday efficiency of NH 3 was as high as 95%, and the overpotential was significantly lower than that of most of the catalysts reported earlier (Figure 3d,e).…”

“…In a study, 150 a series of SAAs formed by embedding a sequence of single transition metal atoms on the surface of Cu (111) were alloyed, and this alloy was denoted as TM/ Cu (111). By analyzing the stability, adsorption energy of NO 3 − , and limiting potential of various TM/Cu (111), the electrochemical nitrate reduction performance of TM/Cu (111) with three elements, namely, Ti, Ni, and Nb, was found to be outstanding, among which Ni/Cu (111) had the highest selectivity. The activities of these three substances depend on the adsorption energy for NO 3 − and the preference for Cu or individual atoms for *N adsorption.…”

Constructing a CoO–CuOx heterostructure for efficient electrochemical reduction of nitrate to ammonia

“…Therefore, developing low-cost, efficient, and durable electrocatalysts for the NtrRR to achieve high FE NH 3 and high NH 3 yield rate, while simultaneously suppressing the side hydrogen evolution reaction (HER), is imperative. 18,19 In the past decade, Earth-abundant metal-element-based materials including Cu, Co and their oxides have been continuously gaining increasing research attention as promising 20,21 In particular, copper-based catalysts such as copper and copper oxide nanomaterials or nanocomposites show strong adsorption capability towards nitrate and exhibit fast reaction kinetics of the rate-determining step of *NO 3 -to-*NO 2 conversion, leading to some intriguing catalytic properties. 22,23 For instance, the Wang group developed a highperformance Cu-nanosheet catalyst, which could deliver a NH 3 partial current density of 665 mA cm −2 and NH 3 yield rate of 1.41 mmol h −1 cm −2 in a ow cell at −0.59 V vs. RHE.…”