Copper-Based Electrocatalysts for Nitrate Reduction to Ammonia.

Ammonia (NH3) is a highly important industrial chemical used as fuel and fertilizer. The industrial synthesis of NH3 relies heavily on the Haber-Bosch route, which accounts for roughly 1.2% of global annual CO2 emissions. As an alternative route, the electrosynthesis of NH3 from nitrate anion (NO3-) reduction (NO3-RR) has drawn increasing attention, since NO3-RR from wastewater to produce NH3 can not only recycle waste into treasure but also alleviate the adverse effects of excessive NO3- contamination in the environment. This review presents contemporary views on the state of the art in electrocatalytic NO3- reduction over Cu-based nanostructured materials, discusses the merits of electrocatalytic performance, and summarizes current advances in the exploration of this technology using different strategies for nanostructured-material modification. The electrocatalytic mechanism of nitrate reduction is also reviewed here, especially with regard to copper-based catalysts.

Ampere-level current density ammonia electrochemical synthesis using CuCo nanosheets simulating nitrite reductase bifunctional nature.

The development of electrocatalysts capable of efficient reduction of nitrate (NO3-) to ammonia (NH3) is drawing increasing interest for the sake of low carbon emission and environmental protection. Herein, we present a CuCo bimetallic catalyst able to imitate the bifunctional nature of copper-type nitrite reductase, which could easily remove NO2- via the collaboration of two active centers. Indeed, Co acts as an electron/proton donating center, while Cu facilitates NOx- adsorption/association. The bio-inspired CuCo nanosheet electrocatalyst delivers a 100 ± 1% Faradaic efficiency at an ampere-level current density of 1035 mA cm-2 at -0.2 V vs. Reversible Hydrogen Electrode. The NH3 production rate reaches a high activity of 4.8 mmol cm-2 h-1 (960 mmol gcat-1 h-1). A mechanistic study, using electrochemical in situ Fourier transform infrared spectroscopy and shell-isolated nanoparticle enhanced Raman spectroscopy, reveals a strong synergy between Cu and Co, with Co sites promoting the hydrogenation of NO3- to NH3 via adsorbed *H species. The well-modulated coverage of adsorbed *H and *NO3 led simultaneously to high NH3 selectivity and yield.

High activity of step sites on Pd nanocatalysts in electrocatalytic dechlorination.

The role of step sites on nanocatalysts in the electrocatalytic dechlorination reaction (ECDR) was studied using 3 Pd nanocatalysts with different densities of step sites, which decreased in the order of: tetrahexahedral Pd{310} nanocrystals (THH Pd{310} NCs) > commercial Pd nanoparticles (Pd black) > cubic Pd{100} NCs. The two well-defined Pd NCs served as model catalysts and were prepared through the electrochemical square-wave potential (SWP) method. The toxic herbicide alachlor was first employed in this study as an objective probe to determine the dechlorination performance, which was quantified by the alachlor removal (Rala), the current efficiency (CEala), and the dechlorination selectivity (Sdes). The experimental results demonstrated that the THH Pd{310} NCs with abundant step sites exhibited much higher electrocatalytic performance compared to the cubic Pd{100} NCs with terrace sites. The combination of cyclic voltammetry studies, electrochemical in situ FTIR analysis, and density functional theory (DFT) calculations revealed that the adsorbed CO bond and generated on the step sites could lower the C-Cl bond splitting barrier, leading to a high ECDR efficiency. Other chlorinated organics with an activated carbon atom were also investigated, which revealed that the superiority of the step sites toward Cl-C bond breaking was particular to the compounds with CO bonds. This study provides a deep understanding of high actvitiy of step sites on Pd NCs in EHDC and a strategy to improve this important environmental electrocatalysis process.

Efficient Dechlorination of α-Halocarbonyl and α-Haloallyl Pollutants by Electroreduction on Bismuth.

The electrocatalytic activity of bismuth considered as a low-cost and green electrode material was studied in reductive dechlorination processes. Cyclic voltammetry analyses showed that the Bi electrode exhibited a high catalytic activity to reduce alachlor, a chlorinated herbicide, in the aqueous medium at different pH values. Bulk electrolyses were performed at different potentials and pH values. Alachlor was reduced in deschloroalachlor, its dechlorinated derivative, with a high selectivity (96%) and a current efficiency of 48%. The reductive dechlorination of other chlorinated compounds with an activated carbon atom was then studied, showing that the bismuth electrode catalyzed the electroreduction of chloroacetamides, α-halocarbonyl, and α-haloallyl pollutants. Cyclic voltammetry experiments allowed us to propose a mechanism explaining the high catalytic activity of bismuth to reduce these families of compounds.