RhNi Bimetallenes with Lattice-Compressed Rh Skin towards Ultrastable Acidic Nitrate Electroreduction.

Harvesting recyclable ammonia (NH3) from acidic nitrate (NO3 -)-containing wastewater requires the utilization of corrosion-resistant electrocatalytic materials with high activity and selectivity towards acidic electrochemical nitrate reduction (NO3ER). Herein, ultrathin RhNi bimetallenes with Rh-skin-type structure (RhNi@Rh BMLs) are fabricated towards acidic NO3ER. The Rh-skin atoms on the surface of RhNi@Rh BMLs experience the lattice compression-induced strain effect, resulting in shortened Rh-Rh bond and downshifted d-band center. Experimental and theoretical calculation results corroborate that Rh-skin atoms can inhibit NO2*/NH2* adsorption-induced Rh dissolution, contributing to the exceptional electrocatalytic durability of RhNi@Rh BMLs (over 400 h) towards acidic NO3ER. RhNi@Rh BMLs also reveal an excellent catalytic performance, boasting a 98.4% NH3 Faradaic efficiency and a 13.4 mg h-1 mgcat -1 NH3 yield. Theoretical calculations reveal that compressive stress tunes the electronic structure of Rh skin atoms, which facilitates the reduction of NO* to NOH* in NO3ER. The practicality of RhNi@Rh BMLs has also been confirmed in an alkaline-acidic hybrid zinc-nitrate battery with a 1.39 V open circuit voltage and a 10.5 mW cm-2 power density. This work offers valuable insights into the nature of electrocatalyst deactivation behavior and guides the development of high-efficiency corrosion-resistant electrocatalysts for applications in energy and environment.

Au Nanowires Decorated Ultrathin Co3 O4 Nanosheets toward Light-Enhanced Nitrate Electroreduction.

Nitrate is a reasonable alternative instead of nitrogen for ammonia production due to the low bond energy, large water-solubility, and high chemical polarity for good absorption. Nitrate electroreduction reaction (NO3 RR) is an effective and green strategy for both nitrate treatment and ammonia production. As an electrochemical reaction, the NO3 RR requires an efficient electrocatalyst for achieving high activity and selectivity. Inspired by the enhancement effect of heterostructure on electrocatalysis, Au nanowires decorated ultrathin Co3 O4 nanosheets (Co3 O4 -NS/Au-NWs) nanohybrids are proposed for improving the efficiency of nitrate-to-ammonia electroreduction. Theoretical calculation reveals that Au heteroatoms can effectively adjust the electron structure of Co active centers and reduce the energy barrier of the determining step (*NO → *NOH) during NO3 RR. As the result, the Co3 O4 -NS/Au-NWs nanohybrids achieve an outstanding catalytic performance with high yield rate (2.661 mg h-1 mgcat -1 ) toward nitrate-to-ammonia. Importantly, the Co3 O4 -NS/Au-NWs nanohybrids show an obviously plasmon-promoted activity for NO3 RR due to the localized surface plasmon resonance (LSPR) property of Au-NWs, which can achieve an enhanced NH3 yield rate of 4.045 mg h-1 mgcat -1 . This study reveals the structure-activity relationship of heterostructure and LSPR-promotion effect toward NO3 RR, which provide an efficient nitrate-to-ammonia reduction with high efficiency.

Oxygen-Vacancy-Rich Cu2O Hollow Nanocubes for Nitrate Electroreduction Reaction to Ammonia in a Neutral Electrolyte.

The electrocatalytic nitrate reduction reaction (NO3--ERR) to ammonia (NH3) is a promising strategy for NH3 production. Cu-based nanomaterials have been regarded as a kind of effective NO3--ERR catalysts. In this work, high-quality hollow Cu2O nanocubes (Cu2O h-NCs) are facilely synthesized by a simple one-step reduction method. The as-prepared Cu2O h-NCs reveal high selectivity and activity for NO3--ERR, which is ascribed to abundant oxygen vacancies, high surface area, hollow architecture, low mass transfer resistance, and strong adsorbing ability toward NO3-. In fact, Cu2O h-NCs can achieve a Faradic efficiency of 92.9% and an NH3 yield of 56.2 mg h-1 mgcat-1 for NH3 production at -0.85 V (vs RHE) potential, which exceeds those of other transition-metal-based NO3--ERR electrocatalysts.

Iron-Doped Cobalt Phosphide Nanohoops for Electroreduction of Nitrate to Ammonia.

Heteroatom doping can effectively tune the electronic structure of an electrocatalyst to accelerate the adsorption/desorption of reaction intermediates, which sharply increases their intrinsic electroactivity. Herein, we successfully prepare iron (Fe)-doped cobalt phosphide (CoP) nanohoops (Fe/CoP NHs) with different Fe/Co atomic ratios as highly active electrocatalysts for the nitrate electrocatalytic reduction reaction (NIT-ERR). Electrochemical measurements reveal that appropriate Fe doping can improve the electroactivity of cobalt phosphide nanohoops for the NIT-ERR. In a 1 M KOH electrolyte, the Fe/CoP NHs with the optimized chemical composition can achieve an efficient ammonia (NH3) generation rate of 27.6 mg h-1 mgcat-1 for the conversion of NO3- into NH3 and a Faradaic efficiency of 93.3% at a -0.25 V potential, which exceed the values of various previously reported nanomaterials in an alkaline electrolyte.

Cobalt phosphide nanorings towards efficient electrocatalytic nitrate reduction to ammonia.

High-quality CoP nanorings (CoP NRs) are easily achieved using a phosphorating treatment of CoOOH nanorings, and reveal high activity towards the hydrogen evolution reaction and the nitrate electrocatalytic reduction reaction due to substantial coordinately unsaturated active sites, a high surface area, and available mass transfer pathways. Consequently, the CoP NRs can achieve a faradaic efficiency of 97.1% towards NO3--to-NH3 conversion and provide an NH3 yield of 30.1 mg h-1 mg-1cat at a -0.5 V potential.

Hydrogen and Potassium Acetate Co-Production from Electrochemical Reforming of Ethanol at Ultrathin Cobalt Sulfide Nanosheets on Nickel Foam.

The sluggish reaction kinetics of the anodic oxygen evolution reaction increases the energy consumption of the overall water electrolysis for high-purity hydrogen generation. In this work, ultrathin cobalt sulfide nanosheets (Co3S4-NSs) on nickel foam (Ni-F) nanohybrids (termed as Co3S4-NSs/Ni-F) are synthesized using cyanogel hydrolysis and a sulfurization two-step approach. Physical characterizations reveal that Co3S4-NSs with a 1.7 nm thickness have abundant holes, implying the big surface area, abundant active edge atoms, and sufficient active sites. Electrochemical measurements show that as-synthesized Co3S4-NSs/Ni-F have excellent electrocatalytic activity and selectivity for ethanol oxidation reaction and hydrogen evolution reaction. Due to their bifunctional property of Co3S4-NSs/Ni-F nanohybrids, a symmetric Co3S4-NSs/Ni-F∥Co3S4-NSs/Ni-F ethanol electrolyzer can be effectively constructed, which only requires a 1.48 V electrolysis voltage to reach a current density of 10 mA cm-2 for high-purity hydrogen generation at the cathode as well as value-added potassium acetate generation at the anode, much lower than the electrolysis voltage of traditional electrochemical water splitting (1.64 V).