Self-Activated Ni Cathode for Electrocatalytic Nitrate Reduction to Ammonia: From Fundamentals to Scale-Up for Treatment of Industrial Wastewater

Abstract

Electrocatalytic reduction has recently received increasing attention as a method of converting waste nitrate into value-added ammonia, but most studies have focused on complex strategies of catalyst preparation and little has been done in the way of large-scale demonstrations. Herein, we report that in situ activation of a pristine Ni electrode, either on a lab scale or a pilot scale, is effective in facilitating nitrate reduction to ammonia, exhibiting extraordinarily high activity, selectivity, and stability. The self-activated Ni cathode has a robust capacity to reduce nitrate over a wide range of concentrations and achieves great conversion yield, NH4 +–N selectivity, and Faradaic efficiency, respectively, 95.3, 95.5, and 64.4% at 200 mg L–1 NO3 ––N and 97.8, 97.1, and 90.4% at 2000 mg L–1 NO3 ––N, for example. Fundamental research indicates that Ni­(OH)2 nanoparticles are formed on the Ni electrode surface upon self-activation, which play crucial roles in governing nitrate reduction reaction (NO3RR) through the atomic H*-mediated pathway and accordingly suppressing hydrogen evolution reaction. More importantly, the self-activated Ni­(OH)2@Ni cathode can be easily scaled up to allow large volumes of real industrial wastewater to be processed, successfully transferring nitrate into ammonia with high yields and Faradaic efficiency. This study demonstrates a new, mild, and promising method of cleaning nitrate-laden wastewater that produces ammonia as a valuable byproduct.

Recent advances in nanostructured heterogeneous catalysts for N-cycle electrocatalysis

“…Indeed, the electrochemical nitrogen reduction reaction (NRR) is so difficult that it has inspired the development of nitrate reduction reaction (NO3RR) and nitric oxide reduction reactions (NORR) to produce NH3 [24]. The use of the more reactive but harmful NO3 − , NO2 − , NO, etc., as precursors can contribute to higher conversion efficiencies and is expected to reduce related environmental pollution [25][26][27][28][29][30][31][32][33][34][35]. Furthermore, as shown in Fig.…”

Tuning Nitrate Electroreduction Activity via an Equilibrium Adsorption Strategy: A Computational Study

“…15 Apart from theoretical assumptions, in situ activation of a pure nickel electrode shows excellent NH 3 yield and Faraday efficiency experimentally. 6 Thus, it can be seen that the exploitation of advanced electrode materials is inseparable from the intervention of TM elements, which have inherent advantages as functional catalysts. Currently, it has become a mainstream strategy to explore suitable substrates to cater to TM coconstructing single atom catalysts featuring 100% atom utilization, low cost, high activity/selectivity, and flexible modulation.…”

“…For example, commonly used explosives such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), and 2,4,6-trinitrotoluene (TNT), etc. contain abundant nitrogen rings/chains, which can produce numerous nitrogen oxides (NO 2 , NO, and N 2 O) in the synthesis or explosion process, resulting in a severe environmental burden. − In addition, the accumulation of the pollutants easily permeates into water bodies or soil to form stable nitrate anions (NO 3 – ), which pose a great threat to people’s health and ecological quality. − Also, the nitrates exist in the explosive industry wastewater. Thereby, it is urgent to seek a reasonable method to dispose of the effluents formed in the use and production of explosives.…”

“…Among them, biodegrading bacterial enzymes have been successfully extracted from plant nodules to promote the degradation of the nitrates; however, their sluggish response efficiency restrains further use . Ion-exchange membrane technology is favored for its targeted physical penetration and considerable processing rates, but costly fabrication and complex external parameters limit its widespread application. , To break the bottleneck and achieve a promising alternative, electrochemical catalysis progress, driven by renewable electricity and featuring remarkable efficiency, has aroused great enthusiasm . Similar to the electrochemical nitrogen reduction reaction (ENRR) technique, , the reduction of the nitrate to value-added ammonia (NH 3 ) is of paramount importance for electrochemical catalysis.…”

Ambient ammonia production via electrocatalytic nitrate reduction catalyzed by a flower-like CuCo2O4 electrocatalyst

“…However, electrocatalysts play the key role in the NtRR and their performance is often evaluated based on three criteria (activity, selectivity, and longevity). 13 Meanwhile, the NtRR competes with the HER, making it difficult to achieve a high yield and high FE. 14 Therefore, it is urgently required to develop catalysts that can selectively promote ammonia production and suppress hydrogen evolution.…”