RESUMEN

Electrocatalytic nitrate reduction to ammonia (NO3RR) is very attractive for nitrate removal and ammonia production in industrial processes. However, the nitrate reduction reaction is characterized by intense hydrogen competition at strong reduction potentials, which greatly limits the Faraday efficiency at strong reduction potentials. Herein, we reported an AuxCu single-atom alloy aerogels (AuxCu SAAs) with three-dimensional network structure with significant nitrate reduction performance of Faraday efficiency (FE) higher than 90% over a wide potential range (0 ~ -1 VRHE). The FE of the catalyst was close to 100% at a high reduction potential of -0.8 VRHE, accompanying with NH3 yield reaching 6.21 mmol h-1 cm-2. More importantly, the catalyst maintained a long-term operation over 400 h at 400 mA cm-2 for the NO3RR using a continuous flow system in a H-cell. Experimental and theoretical analysis demonstrate that the catalyst can lower the energy barrier for the hydrogenation reaction of *NO2, leading to a rapid consumption of the generated *H, facilitate the hydrogenation process of NO3RR, and inhibit the competitive HER at high overpotentials, which efficiently promotes the nitrate reduction reaction, especially in industrial applications.

RESUMEN

Electrochemical nitrate reduction reaction (NO3-RR) has promising prospects for green synthesis of ammonia and environmental remediation. However, the performance of catalysts at high current density usually suffers from the high energy barrier for the nitrate (NO3-) to nitrite (NO2-) and the competitive hydrogen evolution. Herein, we proposed a two-step relay mechanism through spontaneous redox reaction followed electrochemical reaction by introducing low-valence Fe species into Ni2P nanosheets to significantly enhance the NO3-RR performance at industrial current density. The existence of low-valence Fe species bypasses the NO3- to NO2- step through the spontaneous redox with NO3- to produce NO2- and Fe2O3, regulates the electronic structure of Ni2P to reduce the barrier of NO2- to NH3, thirdly prohibits the hydrogen evolution by consuming the excess active hydrogen through reduction of Fe2O3 to recover low-valence Fe species. The triple regulations via Fe redox during the two-step relay reactions guarantee the Fe-Ni2P@NF high ammonia yield of 120.1 mg h-1 cm-2 with Faraday efficiency of more than 90% over a wide potential window and a long-term stability of more than 130 h at ~1000 mA cm-2. This work provides a new strategy to realize the design and synthesis of nitrate reduction electrocatalysts at high current densities.

RESUMEN

Electrochemical NO3- reduction reaction (NO3RR) represents a green and sustainable way to produce valuable NH3 for both NH3 production and nitrate contaminant removal, and developing efficient, durable, highly selective catalyst is the key. Herein, we report a facile method to fabricate a catalyst composed of ultrafine Cu nanowires (Cu NWs) encapsulated by ZIF67, namely, CuNW@ZIF67, for efficient NH3 electrosynthesis from nitrate. The CuNW@ZIF67 catalyst exhibited excellent catalytic performance toward NO3RR in alkaline electrolyte, manifested by a large NH3 Faradaic efficiency of 93.7% at -0.5 V versus reversible hydrogen electrode (RHE), a high energy efficiency over 30% at -0.7 V, and robust long-term stability. Such intriguing catalytic properties are mainly ascribed to its structural merits and the strong electronic interaction between Cu NWs and ZIF67. DFT calculations revealed that, the Cu site can easily convert NO3- into NO2-, while the Co site plays a critical role in catalyzing the NO2--to-NH3 process. The study can shed light on rational design of efficient, durable, and highly selective catalysts for NO3RR and beyond.

RESUMEN

Electrochemical conversion of nitrate (NO3 -) to ammonia (NH3) is an effective approach to reduce nitrate pollutants in the environment and also a promising low-temperature, low-pressure method for ammonia synthesis. However, adequate H* intermediates are highly expected for NO3 - hydrogenation, while suppressing competitive hydrogen evolution. Herein, the effect of H* coverage on the NO3RR for ammonia synthesis by Cu electrocatalysts is investigated. The H* coverage can be adjusted by changing Pd nanoparticle sizes. The optimized Pd@Cu with an average Pd size of 2.88 nm shows the best activity for NO3RR, achieving a maximum Faradaic efficiency of 97% (at -0.8 V vs RHE) and an NH3 yield of 21 mg h-1 cm- 2, from an industrial wastewater level of 500 ppm NO3 -. In situ electrochemical experiments indicate that Pd particles with 2.88 nm can promote NO3 - hydrogenation to NH3 via well-modulated coverage of adsorbed H* species. Coupling the anodic glycerol oxidation reaction, ammonium and formate are successfully obtained as value-added products in a membrane electrode assembly electrolyzer. This work provides a feasible strategy for obtaining size-dependent H* intermediates for hydrogenation.

RESUMEN

Electrochemical nitrate reduction reaction (NO3-RR) is a promising low-carbon and environmentally friendly approach for the production of ammonia (NH3). Herein, we develop a high-temperature quenched copper (Cu) catalyst with the aim of inducing nonequilibrium phase transformation, revealing the multiple defects (distortion, dislocations, vacancies, etc.) presented in Cu, which lead to low overpotential for NO3-RR and high efficiency for NH3 production. Further loading a low content of iridium (Ir) species on the Cu surface improves the reactivity and ammonia selectivity. The resultant CuIr electrode exhibits a Faradaic efficiency of 93% and a record yield of 6.01 mmol h-1 cm-2 at -0.22 VRHE exceeding those of state-of-the-art NO3-RR catalysts. Detailed investigations have demonstrated that the synergistic effect between multiple defects and Ir decoration effectively regulate the d-band center of copper, change the adsorption state of the catalyst surface, and promote the adsorption and reduction of intermediates and reactants. The strong H* adsorption ability of the Ir element provides more active hydrogen for the generation of ammonia, promoting the reduction of nitrate to NH3.

RESUMEN

Electrochemical nitrate (NO3-) reduction reaction (NO3-RR) to ammonium (NH4+) or nitrogen (N2) provides a green route for nitrate remediation. However, nitrite generation and hydrogen evolution reactions hinder the feasibility of the process. Herein, dual single atom catalysts were rationally designed by introducing Ag/Bi/Mo atoms to atomically dispersed NiNC moieties supported by nitrogen-doped carbon nanosheet (NCNS) for the NO3-RR. Ni single atoms loaded on NCNS (Ni/NCNS) tend to reduce NO3- to valuable NH4+ with a high selectivity of 77.8 %. In contrast, the main product of NO3-RR catalyzing by NiAg/NCNS, NiBi/NCNS, and NiMo/NCNS was changed to N2, giving rise to N2 selectivity of 48.4, 47.1 and 47.5 %, respectively. Encouragingly, Ni/NCNS, NiBi/NCNS, and NiAg/NCNS showed excellent durability in acidic electrolytes, leading to nitrate conversion rates of 70.3, 91.1, and 93.2 % after a 10-h reaction. Simulated wastewater experiments showed that NiAg/NCNS could remove NO3- up to 97.8 % at -0.62 V after 9-h electrolysis. This work afforded a new strategy to regulate the reaction pathway and improve the conversion efficiency of the NO3-RR via engineering the dual atomic sites of the catalysts.

RESUMEN

Electrochemical nitrate reduction to ammonia (NRA) is a promising approach to remove environmental pollutants while producing green NH3 under ambient conditions. Ag-based nanomaterials have been used in NRA but their iron series elements (Fe, Co, Ni) doping has not been explored yet. Herein, an effective and versatile doping strategy of Ag nanocrystals by iron series elements for efficient NRA is presented. Experimental results show that doping with Fe, Co or Ni can improve the NRA activity. Among the catalysts, AgCo delivers the best performance with a Faraday efficiency (FE) of 88.3 % and ammonia selectivity of 97.4 % at-0.23 V vs RHE, which is 1.9 and 6.2 times higher than that of plain Ag (46.4 % FE and 15.8 % selectivity), respectively. A highest NO3 - conversion rate of AgCo (91.8 %) is achieved, which maintains 16.4 ppm NO3 --N in 4 hours, meeting the drinking water level (~15 ppm NO3 --N). Moreover, the FE, selectivity, conversion rate of AgCo do not decay after the four consecutive cycles. It is found that Co doping can effectively induce the change of Ag d-band center for optimized NRA. This work reveals doping effects of iron series elements on Ag-based catalysts, and shows potential practical application in NRA.

RESUMEN

Electrode scaling poses a critical barrier to the adoption of electrochemical processes in wastewater treatment, primarily due to electrode inactivation and increased internal reactor resistance. We introduce an antiscaling strategy using tip-enhanced electric fields to redirect scale-forming compounds (e.g., Mg(OH)2 and CaCO3) from the electrode-electrolyte interface to the bulk solution. Our study utilized Cu nanowires (Cu NW) with high-curvature nanostructures as the cathode, in contrast to Cu nanoparticles (Cu NP), Cu foil (CF), and Cu mesh (CM), to evaluate the electrochemical nitrate reduction reaction (NO3RR) performance in hard water conditions. The Cu NW/CF cathode demonstrated superior NO3RR efficiency, with an apparent rate constant (Kapp) of 1.04 h-1, significantly outperforming control electrodes under identical conditions (Kapp < 0.051 h-1). Through experimental and theoretical analysis, including COMSOL simulations, we show that the high-curvature design of Cu NW induced localized electric field enhancements, propelling OH- ions away from the electrode surface into the bulk solution, thus mitigating scale formation on the cathode. Testing with real nitrate-contaminated wastewater confirms that the Cu NW/CF cathode maintained excellent denitrification efficiency over a 60-day period. This study offers a promising perspective on preventing electrode scaling in electrochemical wastewater treatment, paving the way for more efficient and sustainable practices.

Asunto(s)

RESUMEN

Electrocatalytic nitrate reduction is an efficient way to produce ammonia sustainably. Herein, we rationally designed a copper metalloporphyrin-based hydrogen-bonded organic framework (HOF-Cu) through molecular engineering strategies for electrochemical nitrate reduction. As a result, the state-of-the-art HOF-Cu catalyst exhibits high NH3 Faradaic efficiency of 93.8%, and the NH3 production rate achieves a superior activity of 0.65 mmol h-1 cm-2. The in situ electrochemical spectroscopic combined with density functional theory calculations reveals that the dispersed Cu promotes the adsorption of NO3- and the mechanism is followed by deoxidation of NO3- to *NO and accompanied by deep hydrogenation. The generated *H participates in the deep hydrogenation of intermediate with fast kinetics as revealed by operando electrochemical impedance spectroscopy, and the competing hydrogen evolution reaction is suppressed. This research provides a promising approach to the conversion of nitrate to ammonia, maintaining the nitrogen balance in the atmosphere.

RESUMEN

Nitrate, a prevalent water pollutant, poses substantial public health concerns and environmental risks. Electrochemical reduction of nitrate (eNO3RR) has emerged as an effective alternative to conventional biological treatments. While extensive lab work has focused on designing efficient electrocatalysts, implementation of eNO3RR in practical wastewater settings requires careful consideration of the effects of various constituents in real wastewater. In this critical review, we examine the interference of ionic species commonly encountered in electrocatalytic systems and universally present in wastewater, such as halogen ions, alkali metal cations, and other divalent/trivalent ions (Ca2+, Mg2+, HCO3-/CO32-, SO42-, and PO43-). Notably, we categorize and discuss the interfering mechanisms into four groups: (1) loss of active catalytic sites caused by competitive adsorption and precipitation, (2) electrostatic interactions in the electric double layer (EDL), including ion pairs and the shielding effect, (3) effects on the selectivity of N intermediates and final products (N2 or NH3), and (4) complications by the hydrogen evolution reaction (HER) and localized pH on the cathode surface. Finally, we summarize the competition among different mechanisms and propose future directions for a deeper mechanistic understanding of ionic impacts on eNO3RR.

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RESUMEN

Electrochemically converting nitrate (NO3 -) into ammonia (NH3) has emerged as an alternative strategy for NH3 production and effluent treatment. Nevertheless, the electroreduction of dilute NO3 - is still challenging due to the competitive adsorption between various aqueous species and NO3 -, and unfavorable water dissociation providing *H. Herein, a new tandem strategy is proposed to boost the electrochemical nitrate reduction reaction (NO3RR) performance of Cu nanoparticles supported on single Fe atoms dispersed N-doped carbon (Cu@Fe1-NC) at dilute NO3 - concentrations (≤100 ppm NO3 --N). The optimized Cu@Fe1-NC presents a FENH3 of 97.7% at -0.4 V versus RHE, and a significant NH3 yield of 1953.9 mmol h-1 gCu -1 at 100 ppm NO3 --N, a record-high activity for dilute NO3RR. The metal/carbon heterojunctions in Cu@Fe1-NC enable a spontaneous electron transfer from Cu to carbon substrate, resulting in electron-deficient Cu. As a result, the electron-deficient Cu facilitates the adsorption of NO3 - compared with the pristine Cu. The adjacent atomic Fe sites efficiently promote water dissociation, providing abundant *H for the hydrogenation of *NOx e at Cu sites. The synergistic effects between Cu and single Fe atom sites simultaneously decrease the energy barrier for NO3 - adsorption and hydrogenation, thereby enhancing the overall activity of NO3 - reduction.

RESUMEN

Electrochemical nitrate reduction (NO3-RR) has been recognized as a promising strategy for sustainable ammonia (NH3) production due to its environmental friendliness and economical nature. However, the NO3-RR reaction involves an eight-electron coupled proton transfer process with many by-products and low Faraday efficiency. In this work, a molybdenum oxide (MoOx)-decorated titanium dioxide nanotube on Ti foil (Mo/TiO2) was prepared by means of an electrodeposition and calcination process. The structure of MoOx can be controlled by regulating the concentration of molybdate during the electrodeposition process, which can further influence the electron transfer from Ti to Mo atoms, and enhance the binding energy of intermediate species in NO3-RR. The optimized Mo/TiO2-M with more Mo(IV) sites exhibited a better activity for NO3-RR. The Mo/TiO2-M electrode delivered a NH3 yield of 5.18 mg h-1 cm-2 at -1.7 V vs. Ag/AgCl, and exhibited a Faraday efficiency of 88.05% at -1.4 V vs. Ag/AgCl. In addition, the cycling test demonstrated that the Mo/TiO2-M electrode possessed a good stability. This work not only provides an attractive electrode material, but also offers new insights into the rational design of catalysts for NO3-RR.

RESUMEN

Electrocatalytic nitrate removal offers a sustainable approach to alleviate nitrate pollution and to boost the anthropogenic nitrogen cycle, but it still suffers from limited removal efficiency at high rates, especially at low levels of nitrate. Herein, we report the near-complete removal of low-level nitrate (10-200 ppm) within 2 h using ultrathin cobalt-based nanosheets (CoNS) containing surface oxygen, which was fabricated from in-situ electrochemical reconstruction of conventional nanosheets. The average nitrate removal of 99.7 % with ammonia selectivity of 98.2 % in 9 cyclic runs ranked in the best of reported catalysts. Powered by a solar cell under the winter sun, the full-cell nitrate electrolysis system, equipped with ultrathin CoNS, achieved 100 % nitrogen gas selectivity and 99.6 % total nitrogen removal. The in-situ Fourier Transform Infrared included experiments and theoretical computations revealed that in-situ electrochemical reconstruction not only increased electrochemical active surface area but also constructed surface oxygen in active sites, leading to enhanced stabilization of nitrate adsorption in a symmetry breaking configuration and charge transfer, contributing to near-complete nitrate removal on ultrathin CoNS. This work provides a strategy to design ultrathin nanocatalysts for nitrate removal.

RESUMEN

Electro-catalytic conversion of nitrate (NO3-) to ammonia (NH3) via the Nitrate Reduction to Ammonia (NORA) process represents a promising strategy for both ammonia synthesis and environmental remediation. Despite its potential, the efficiency of low-concentration NORA is often hindered by mass transfer limitations, competing byproducts (N2 and NO2-), and side reactions such as hydrogen evolution. This study introduces a novel pulsed electro-synthesis technique that alternates the potential to periodically accumulate and transform NO2- intermediates near a Cu2O@Pd electrode, enhancing the NORA process. Compared with that under potentiostatic conditions, the Cu2O@Pd electrodes exhibited a higher NORA activity under the optimized pulsed condition, where a NH3-N Faradaic efficiency (FE) of 81.2%, a yield rate of 1.08 mg h-1 cm-2 and a selectivity efficiency (SE) of 81.5%, were achieved. In-situ characterization revealed an enhancement mechanism characterized by optimized adsorption of the key *NO intermediate, followed by the hydrogenation path "*N → *NH → *NH2→ *NH3". Further investigations indicated the electro-catalytic synergies between Pd sites and Cu species, where the Pd atoms were the reaction sites for the H adsorption while the Cu species were responsible for the NO3- activation. This research offers a novel insight into a method of enhancing low-concentration NORA.

RESUMEN

The electronic states of metal catalysts can be redistributed by the rectifying contact between metal and semiconductor e.g., N-doped carbon (NC), while the interfacial regulation degree is very limited. Herein, a deep electronic state regulation is achieved by constructing a novel double-heterojunctional Co/Co3O4@NC catalyst containing Co/Co3O4 and Co3O4/NC heterojunctions. When used for dilute electrochemical NO3 - reduction reaction (NO3RR), the as-prepared Co/Co3O4@NC exhibits an outstanding Faradaic efficiency for NH3 formation (FENH3) of 97.9%, -0.4 V versus RHE and significant NH3 yield of 303.5 mmol h-1 gcat -1 at -0.6 V at extremely low nitrate concentrations (100 ppm NO3 --N). Experimental and theoretical results reveal that the dual junctions of Co/Co3O4 and Co3O4/NC drive a unidirectional electron transfer from Co to NC (Co→Co3O4→NC), resulting in electron-deficient Co atoms. The electron-deficient Co promotes NO3 - adsorption, the rate-determining step (RDS) for NO3RR, facilitating the dilute NO3RR to NH3. The design strategy provides a novel reference for unidirectional multistage regulation of metal electronic states boosting electrochemical dilute NO3RR, which opens up an avenue for deep electronic state regulation of electrocatalyst breaking the limitation of the electronic regulation degree by rectifying contact.

RESUMEN

The development of electrocatalysts that can efficiently reduce nitrate (NO3-) to ammonia (NH3) has garnered increasing attention due to their potential to reduce carbon emissions and promote environmental protection. Intensive efforts have focused on catalyst development, but a thorough understanding of the effect of the microenvironment around the reactive sites of the catalyst is also crucial to maximize the performance of the electrocatalysts. This study explored an electrocatalytic system that utilized quaternary ammonium surfactants with a range of alkyl chain lengths to modify an electrode made of carbon nanotubes (CNT), with the goal of regulating interfacial wettability toward NO3- reduction. Trimethyltetradecylammonium bromide with a moderate alkyl chain length created a very hydrophobic interface, which led to a high selectivity in the production of NH3 (∼87%). Detailed mechanistic investigations that used operando Fourier-transform infrared (FTIR) spectroscopy and online differential electrochemical mass spectrometry (DEMS) revealed that the construction of a hydrophobic modified CNT played a synergistic role in suppressing a side reaction involving the generation of hydrogen, which would compete with the reduction of NO3-. This electrocatalytic system led to a favorable process for the reduction of NO3- to NH3 through a direct electron transfer pathway. Our findings underscore the significance of controlling the hydrophobic surface of electrocatalysts as an effective means to enhance electrochemical performance in aqueous media.

Asunto(s)

RESUMEN

Electrochemical reduction of nitrate to ammonia (NO3RR) is a promising and eco-friendly strategy for ammonia production. However, the sluggish kinetics of the eight-electron transfer process and poor mechanistic understanding strongly impedes its application. To unveil the internal laws, herein, a library of Pd-based bimetallene with various transition metal dopants (PdM (M=Fe, Co, Ni, Cu)) are screened to learn their structure-activity relationship towards NO3RR. The ultra-thin structure of metallene greatly facilitates the exposure of active sites, and the transition metals dopants break the electronic balance and upshift its d-band center, thus optimizing intermediates adsorption. The anisotropic electronic characteristics of these transition metals make the NO3RR activity in the order of PdCu>PdCo≈PdFe>PdNi>Pd, and a record-high NH3 yield rate of 295 mg h-1 mgcat -1 along with Faradaic efficiency of 90.9 % is achieved in neutral electrolyte on PdCu bimetallene. Detailed studies further reveal that the moderate N-species (*NO3 and *NO2) adsorption ability, enhanced *NO activation, and reduced HER activity facilitate the NH3 production. We believe our results will give a systematic guidance to the future design of NO3RR catalysts.

RESUMEN

The electrochemical upcycling of nitrate (NO3-) to ammonia (NH3) holds promise for synergizing both wastewater treatment and NH3 synthesis. Efficient stripping of gaseous products (NH3, H2, and N2) from electrocatalysts is crucial for continuous and stable electrochemical reactions. This study evaluated a layered electrocatalyst structure using copper (Cu) dendrites to enable a high curvature and hydrophobicity and achieve a stratified liquid contact at the gas-liquid interface of the electrocatalyst layer. As such, gaseous product desorption or displacement from electrocatalysts was enhanced due to the separation of a wetted reaction zone and a nonwetted zone for gas transfer. Consequently, this electrocatalyst structure yielded a 2.9-fold boost in per-active-site activity compared with that with a low curvature and high hydrophilic counterpart. Moreover, a NH3 Faradaic efficiency of 90.9 ± 2.3% was achieved with nearly 100% NO3- conversion. This high-curvature hydrophobic Cu dendrite was further integrated with a gas-extraction membrane, which demonstrated a comparable NH3 yield from the real reverse osmosis retentate brine.

RESUMEN

Despite the great potential of electrochemical nitrate reduction as a hydroxylamine production method, this strategy has not been sufficiently examined, and the effects of electrode material type on the selectivity and efficiency of this reduction remain underexplored. To bridge this gap, the present study evaluated six metals (Ag, Cu, Ni, Sn, Ti, and Zn) as cathode materials for the electrochemical reduction of nitrate to hydroxylamine, showing that the selectivity of hydroxylamine production was maximal for Sn, while the corresponding faradaic and energy utilization efficiencies were maximal for Ti. Although all tested materials favored nitrate reduction over hydrogen evolution, the disparity in the onset potentials of these reactions did not adequately explain the variations in nitrate removal efficiency, which was found to be influenced by material resistance and charge-transfer properties. The rate constants of elementary nitrate reduction steps determined from the time-dependent concentrations of nitrate and its reduction products (nitrous acid, hydroxylamine, and ammonium) were used to calculate the selectivity and efficiency of hydroxylamine production for each electrode. In turn, these selectivities and efficiencies were correlated with the density functional theory-computed adsorption energies of a key hydroxylamine precursor on different electrodes to afford a volcano-type plot with Ti and Sn at its pinnacle. Thus, this study introduces valuable descriptors and methods for the further screening of electrocatalysts for hydroxylamine generation and the establishment of more environmentally friendly hydroxylamine production techniques utilizing sustainable electricity.

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RESUMEN

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.