Sustainable conversion of alkaline nitrate to ammonia at activities greater than 2 A cm-2

Nitrate (NO3‒) pollution poses significant threats to water quality and global nitrogen cycles. Alkaline electrocatalytic NO3‒ reduction reaction (NO3RR) emerges as an attractive route for enabling NO3‒ removal and sustainable ammonia (NH3) synthesis. However, it suffers from insufficient proton (H+) supply in high pH conditions, restricting NO3‒-to-NH3 activity. Herein, we propose a halogen-mediated H+ feeding strategy to enhance the alkaline NO3RR performance. Our platform achieves near-100% NH3 Faradaic efficiency (pH = 14) with a current density of 2 A cm-2 and enables an over 99% NO3--to-NH3 conversion efficiency. We also convert NO3‒ to high-purity NH4Cl with near-unity efficiency, suggesting a practical approach to valorizing pollutants into valuable ammonia products. Theoretical simulations and in situ experiments reveal that Cl-coordination endows a shifted d-band center of Pd atoms to construct local H+-abundant environments, through arousing dangling O-H water dissociation and fast *H desorption, for *NO intermediate hydrogenation and finally effective NO3‒-to-NH3 conversion.

Single-atom catalysts supported on a hybrid structure of boron nitride/graphene for efficient nitrogen fixation via synergistic interfacial interactions

Hexagonal boron nitride (BN) shows significant chemical stability and promising thermal nitrogen reduction reaction (NRR) activity but suffers from low conductivity in electrolysis with a wide band gap. To overcome this problem, two-dimensional (2D) BN and graphene (G) are designed as a heterostructure, namely BN/G. According to density functional theory (DFT), the higher conductivity of G narrows the band gap of BN by inducing some electronic states near the Fermi energy level (Ef). Once transition metals (TMs) are anchored in the BN/G structure as single atom catalysts (SACs), the NRR activity improves as the inert BN basal layer activates with moderate *NH2 binding energy and further the band gap is reduced to zero. V (vanadium) and W (tungsten) SACs exhibit the best performance with limiting potentials of -0.22 and -0.41 V, respectively. This study helps in understanding the improvement of the NRR activity of BN, providing physical insights into the adsorbate-TM interaction.

Bifunctional bimetallic oxide nanowires for high-efficiency electrosynthesis of 2,5-furandicarboxylic acid and ammonia

It is an appealing avenue for electrosyntheis of high-valued chemicals at both anode and cathode by coupling 5-hydroxymethylfurfural (HMF) oxidation and nitrate reduction reactions simultaneously, while the development such bifunctional electrocatalysts is still in its infancy with dissatisfied selectivity and low yield rate. Here, we first report that Zn-doped Co3O4 nanowires array can be served as an efficient and robust dual-functional catalyst for HMF oxidation and nitrate reduction at ambient conditions. Specifically, the catalyst shows a faradaic efficiency of 91 % and a yield rate of 241.2 μmol h-1 cm-2 for 2,5-furandicarboxylic acid formation together with a high conversion of nearly 100 % at a potential of 1.40 V. It also displays good cycling stability. Besides, the catalyst is capable of catalyzing the reduction of nitrate to NH3, giving a maximal faradaic efficiency of 92 % and a peak NH3 yield rate of 4.65 mg h-1 cm-2 at a potential of -0.70 V. These results surpass those obtained using pristine Co3O4 and are comparable to those of state-of-the-art electrocatalysts. Moreover, the catalyst is further employed as the cathode catalyst to assemble a Zn-nitrate battery, giving a peak power density of 5.24 mW cm-2 and a high yield rate of 0.72 mg h-1 cm-2. Theoretical simulations further reveal that Zn-doping favors the adsorption and dissociation of nitrate and HMF species and reduces the energy barrier as well. Our work demonstrates the potential interest of Co3O4-based materials for the highly selective production of valuable feedstocks via ambient electrolysis.

Porous and Partially Dehydrogenated Fe2+ -Containing Iron Oxyhydroxide Nanosheets for Efficient Electrochemical Nitrogen Reduction Reaction (ENRR)

The design and development of efficient catalysts for electrochemical nitrogen reduction reaction (ENRR) under ambient conditions are critical for the alternative ammonia (NH3 ) synthesis from N2 and H2 O, wherein iron-based electrocatalysts exhibit outstanding NH3 formation rate and Faradaic efficiency (FE). Here, the synthesis of porous and positively charged iron oxyhydroxide nanosheets by using layered ferrous hydroxide as a starting precursor, which undergoes topochemical oxidation, partial dehydrogenated reaction, and final delamination, is reported. As the electrocatalyst of ENRR, the obtained nanosheets with a monolayer thickness and 10-nm mesopores display exceptional NH3 yield rate (28.5 µg h-1 mgcat. -1 ) and FE (13.2%) at a potential of -0.4 V versus RHE in a phosphate buffered saline (PBS) electrolyte. The values are much higher than those of the undelaminated bulk iron oxyhydroxide. The larger specific surface area and positive charge of the nanosheets are beneficial for providing more exposed reactive sites as well as retarding hydrogen evolution reaction. This study highlights the rational control on the electronic structure and morphology of porous iron oxyhydroxide nanosheets, expanding the scope of developing non-precious iron-based highly efficient ENRR electrocatalysts.

Fundamentals, rational catalyst design, and remaining challenges in electrochemical NOx reduction reaction

Nitrogen oxides (NOx) emissions carry pernicious consequences on air quality and human health, prompting an upsurge of interest in eliminating them from the atmosphere. The electrochemical NOx reduction reaction (NOxRR) is among the promising techniques for NOx removal and potential conversion into valuable chemical feedstock with high conversion efficiency while benefiting energy conservation. However, developing efficient and stable electrocatalysts for NOxRR remains an arduous challenge. This review provides a comprehensive survey of recent advancements in NOxRR, encompassing the underlying fundamentals of the reaction mechanism and rationale behind the design of electrocatalysts using computational modeling and experimental efforts. The potential utilization of NOxRR in a Zn-NOx battery is also explored as a proof of concept for concurrent NOx abatement, NH3 synthesis, and decarbonizing energy generation. Despite significant strides in this domain, several hurdles still need to be resolved in developing efficient and long-lasting electrocatalysts for NOx reduction. These possible means are necessary to augment the catalytic activity and electrocatalyst selectivity and surmount the challenges of catalyst deactivation and corrosion. Furthermore, sustained research and development of NOxRR could offer a promising solution to the urgent issue of NOx pollution, culminating in a cleaner and healthier environment.

Corrosion Engineering towards NiFe-Layered Double Hydroxide Macroporous Arrays with Enhanced Activity and Stability for Oxygen Evolution Reaction

NiFe-layered double hydroxide (NiFe-LDH) is the benchmark catalyst for the oxygen evolution reaction (OER) in alkaline medium, however, it is still challenging to improve its activity and stability. Herein, NiFe-LDH macroporous array electrodes are demonstrated to significantly enhance the activity and stability for oxygen evolution reaction. The electrodes are fabricated by the chemical and electrochemical corrosion process of Ni foam induced by ferric nitrate, hydrochloric acid and oxygen. By optimizing the amount of iron salt and acid and selecting the appropriate reaction temperature and time, the NiFe-LDH electrodes only need the overpotential of 180 mV and 248 mV to reach the current density of 10 mA cm-2 and 500 mA cm-2 , respectively, and remain highly stable for 1000 h at 500 mA cm-2 . The unique macroporous array not only significantly increases the active area of NiFe-LDH catalyst, but also creates a stable nanostructure that avoids severe reconstruction.

Single atomic cerium sites anchored on nitrogen-doped hollow carbon spheres for highly selective electroreduction of nitric oxide to ammonia

Electrocatalytic nitric oxide reduction reaction (NORR) at ambient environments not only offers a promising strategy to yield ammonia (NH₃) but also degrades the NO contaminant; however, its application depends on searching for high-performance catalysts. Herein, we present single atomic Ce sites anchored on nitrogen-doped hollow carbon spheres that are capable of electro-catalyzing NO reduction to NH₃ in an acidic solution, achieving a maximal Faradaic efficiency of 91 % and a yield rate of 1023 μg h^-1 mg_cat.^-1 at -0.7 V vs RHE for NH₃ formation, both of which outperform these on Ce nanoclusters and approach the best-reported results. Meanwhile, the single atomic Ce catalyst shows good structural and electrochemical stability during the 30-h NO electrolysis. Furthermore, when the single atomic Ce catalyst was used as cathodic material in a proof-of-concept of Zn-NO battery, it delivers a maximal power density of 3.4 mW cm^-2 and a high NH₃ yield rate of 309 μg h^-1 mg_cat.^-1. Theoretical simulations suggest that the Ce-N4 active moiety can not only activate NO molecules via a strong electronic interaction but also reduce the free energy barrier of *NO transition to *NOH intermediate as the limiting step, and therefore boosting the NORR kinetics and suppressing the competitive hydrogen evolution.

Efficient electrochemical NO reduction to NH3 over metal-free g-C3N4 nanosheets and the role of interface microenvironment

The ever-increasing NO emission has caused severe environmental issues and adverse effects on human health. Electrocatalytic reduction is regarded as a win-win technology for NO treatment with value-added NH₃ generation, but the process is mainly relied on the metal-containing electrocatalysts. Here, we developed metal-free g-C₃N₄ nanosheets (deposited on carbon paper, named as CNNS/CP) for NH₃ synthesis from electrochemical NO reduction under ambient condition. The CNNS/CP electrode afforded excellent NH₃ yield rate of 15.1 μmol h^-1 cm^-2 (2180.1 mg g_cat^-1 h^-1) and Faradic efficiency (FE) of ∼41.5 % at - 0.8 and - 0.6 V_RHE, respectively, which were superior to the block g-C₃N₄ particles and comparable to the most of metal-containing catalysts. Moreover, through adjusting the interface microenvironment of CNNS/CP electrode by hydrophobic treatment, the abundant gas-liquid-solid triphasic interface improved NO mass transfer and availability, which enhanced NH₃ production and FE to about 30.7 μmol h^-1 cm^-2 (4424.2 mg g_cat^-1 h^-1) and 45.6 % at potential of - 0.8 V_RHE. This study opens a novel pathway to develop efficient metal-free electrocatalysts for NO electroreduction and highlights the importance of electrode interface microenvironment in electrocatalysis.

Recent Progress in Metal Phosphorous Chalcogenides: Potential High-Performance Electrocatalysts

Since the discovery of graphene, research on the family of 2D materials has been a thriving field. Metal phosphorous chalcogenides (MPX₃ ) have attracted renewed attention due to their distinctive physical and chemical properties. The advantages of MPX₃ , such as tunable layered structures, unique electronic properties, thermodynamically appropriate band alignments and abundant catalytic active sites on the surface, make MPX₃ material great potential in electrocatalysis. In this review, the applications of MPX₃ electrocatalysts in recent years, including hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction, are summarized. Structural regulation, chemical doping and multi-material composite that are often effective and practical research methods to further optimize the catalytic properties of these materials, are introduced. Finally, the challenges and opportunities for electrocatalytic applications of MPX₃ materials are discussed. This report aims to advance future efforts to develop MPX₃ and related materials for electrocatalysis.

Volatile organic compound removal by post plasma-catalysis over porous TiO2 with enriched oxygen vacancies in a dielectric barrier discharge reactor

Non-thermal plasma (NTP) degradation of volatile organic compounds (VOCs) into CO₂ and H₂O is a promising strategy for addressing ever-growing environment pollution. However, its practical implementation is hindered by low conversion efficiency and emissions of noxious by-products. Herein, an advanced low-oxygen-pressure calcination process is developed to fine-tune the oxygen vacancy concentration of MOF-derived TiO₂ nanocrystals. Vo-poor and Vo-rich TiO₂ catalysts were placed in the back of an NTP reactor to convert harmful ozone molecules into ROS that decompose VOCs via heterogeneous catalytic ozonation processes. The results indicate that Vo-TiO₂-5/NTP with the highest Vo concentration exhibited superior catalytic activity in the degradation of toluene compared to NTP-only and TiO₂/NTP, achieving a maximum 96% elimination efficiency and 76% CO_x selectivity at an SIE of 540 J L^-1. Mechanistic analysis reveals that the ¹O₂, ˙O₂^- and ˙OH species derived from the activation of O₃ molecules on Vo sites contribute to the decomposition of toluene over the Vo-rich TiO₂ surface. With the aid of advanced characterization and density functional theory calculations, the roles of oxygen vacancies in manipulating the synergistic capability of post-NTP systems were explored, and were attributed to increased O₃ adsorption ability and enhanced charge transfer dynamics. This work presents novel insights into the design of high-efficiency NTP catalysts structured with active Vo sites.

Heterogeneous Ni-MoN nanosheet-assembled microspheres for urea-assisted hydrogen production

Electrocatalytic water splitting is a promising technology for sustainable hydrogen (H₂) production; however, it is restricted by the kinetically sluggish anodic oxygen evolution reaction (OER). Replacing OER with urea oxidation reaction (UOR) with low thermodynamic potential can simultaneously improve the energy efficiency of H₂ production and purify urea-containing wastewater. Here we report a facile assembly-calcination two-step method to synthesize heterogeneous Ni-MoN nanosheet-assembled microspheres (Ni-MoN NAMs). The nanosheet-assembled structure and the synergistic metallic Ni-MoN heterogeneous interface endow the Ni-MoN NAMs with good OER (1.52 V@10 mA cm^-2), UOR (1.28 V@10 mA cm^-2), and hydrogen evolution reaction (HER, 0.16 V@10 mA cm^-2) activity. The two-electrode urea electrolysis cell with Ni-MoN NAMs as both the cathode and anode requires an extremely low cell voltage of 1.41 V to afford 20 mA cm^-2, which is 0.3 V lower than that of the water electrolyzer, paving the way for energy-saving H₂ production.

Cathode materials for halide-based aqueous redox flow batteries: recent progress and future perspectives

As the population increases sharply around the globe, huge shortages are occurring in energy resources. Renewable resources are urgently required to be developed to satisfy human demands. Unlike the lithium-ion batteries with safety and cost issues, the redox flow battery (RFB) is economical, stable, and convenient for the development of large-scale stationary electrical energy storage applications. Especially, the aqueous redox flow battery (ARFB) further exhibits a promising potential in larger power grids owing to its unique structural features of storing energy by filling the tank with electrolytes. The ARFB is capable of modulating battery parameters by controlling the volume and concentration of the electro-active species (EAS). Further, halogens show excellent properties, such as low cost and appropriate potential as an EAS for ARFB, further showing an efficient, safe, and affordable energy storage system (ESS). Moreover, to attain the demands of strong activity, high sensitivity, convenience as well as practicality, further attention needs to be paid to material (electrode) design and adjustment. In this mini-review, novel electrode materials, including their potential internal mechanisms and effective regulatory means, are summarized and applied in the zinc-halogen, hydrogen-halogen, and polysulfide-halogen ARFB systems, promoting the development of valuable material systems and the innovation of the energy storage/conversion technologies.

Self-Supported Pd Nanorod Arrays for High-Efficient Nitrate Electroreduction to Ammonia

Electrochemical nitrate (NO₃ ^- ) reduction to ammonia (NH₃ ) offers a promising pathway to recover NO₃ ^- pollutants from industrial wastewater that can balance the nitrogen cycle and sustainable green NH₃ production. However, the efficiency of electrocatalytic NO₃ ^- reduction to NH₃ synthesis remains low for most of electrocatalysts due to complex reaction processes and severe hydrogen precipitation reaction. Herein, high performance of nitrate reduction reaction (NO₃ ^- RR) is demonstrated on self-supported Pd nanorod arrays in porous nickel framework foam (Pd/NF). It provides a lot of active sites for H* adsorption and NO₃ ^- activation leading to a remarkable NH₃ yield rate of 1.52 mmol cm^-2  h^-1 and a Faradaic efficiency of 78% at -1.4 V versus RHE. Notably, it maintains a high NH₃ yield rate over 50 cycles in 25 h showing good stability. Remarkably, large-area Pd/NF electrode (25 cm² ) shows a NH₃ yield of 174.25 mg h^-1 , be promising candidate for large-area device for industrial application. In situ FTIR spectroscopy and density functional theory calculations analysis confirm that the enrichment effect of Pd nanorods encourages the adsorption of H species for ammonia synthesis following a hydrogenation mechanism. This work brings a useful strategy for designing NO₃ ^- RR catalysts of nanorod arrays with customizable compositions.

One-Step Phase Separation for Core-Shell Carbon@Indium Oxide@Bismuth Microspheres with Enhanced Activity for CO2 Electroreduction to Formate

It is a substantial challenge to construct electrocatalysts with high activity, good selectivity, and long-term stability for electrocatalytic reduction of carbon dioxide to formic acid. Herein, bismuth and indium species are innovatively integrated into a uniform heterogeneous spherical structure by a neoteric quasi-microemulsion method, and a novel C@In₂ O₃ @Bi₅₀ core-shell structure is constructed through a subsequent one-step phase separation strategy due to melting point difference and Kirkendall effect with the nano-limiting effect of the carbon structure. This core-shell C@In₂ O₃ @Bi₅₀ catalyst can selectively reduce CO₂ to formate with high selectivity (≈90% faradaic efficiency), large partial current density (24.53 mA cm^-2 at -1.36 V), and long-term stability (up to 14.5 h), superior to most of the Bi-based catalysts. The hybrid Bi/In₂ O₃ interfaces of core-shell C@In₂ O₃ @Bi will stabilize the key intermediate HCOO* and suppress CO poisoning, benefiting the CO₂ RR selectivity and stability, while the internal cavity of core-shell structure will improve the reaction kinetics because of the large specific surface area and the enhancement of ion shuttle and electron transfer. Furthermore, the nano-limited domain effect of outmost carbon prevent active components from oxidation and agglomeration, helpful for stabilizing the catalyst. This work offers valuable insights into core-shell structure engineering to promote practical CO₂ conversion technology.

Electrocatalytic NO Reduction to NH3 on Mo2C Nanosheets

Electrocatalytic reduction of NO to NH₃ (NORR) emerges as a promising route for achieving harmful NO treatment and sustainable NH₃ generation. In this work, we first report that Mo₂C is an active and selective NORR catalyst. The developed Mo₂C nanosheets deliver a high NH₃ yield rate of 122.7 μmol h^-1 cm^-2 with an NH₃ Faradaic efficiency of 86.3% at -0.4 V. Theoretical computations unveil that the surface-terminated Mo atoms on Mo₂C can effectively activate NO, promote protonation energetics, and suppress proton adsorption, resulting in high NORR activity and selectivity of Mo₂C.

Asymmetric Coordination Environment Engineering of Atomic Catalysts for CO2 Reduction

Single-atom catalysts (SACs) have emerged as well-known catalysts in renewable energy storage and conversion systems. Several supports have been developed for stabilizing single-atom catalytic sites, e.g., organic-, metal-, and carbonaceous matrices. Noticeably, the metal species and their local atomic coordination environments have a strong influence on the electrocatalytic capabilities of metal atom active centers. In particular, asymmetric atom electrocatalysts exhibit unique properties and an unexpected carbon dioxide reduction reaction (CO₂RR) performance different from those of traditional metal-N₄ sites. This review summarizes the recent development of asymmetric atom sites for the CO₂RR with emphasis on the coordination structure regulation strategies and their effects on CO₂RR performance. Ultimately, several scientific possibilities are proffered with the aim of further expanding and deepening the advancement of asymmetric atom electrocatalysts for the CO₂RR.

A dual-functional Bi-doped Co3O4 nanosheet array towards high efficiency 5-hydroxymethylfurfural oxidation and hydrogen production

Here, we report that a Bi-doped Co₃O₄ nanosheet array grown on Ni foam can selectively catalyze HMF-to-FDCA oxidation at ambient conditions. The catalyst shows a faradaic efficiency of 97.7%, a yield rate of 362.5 μmol h^-1, and a conversion of nearly 100%, surpassing those of pristine Co₃O₄. Furthermore, when the catalyst was adopted as both the anode and cathode in a two-electrode system, H₂ and FDCA can be produced simultaneously.

Universal Synthesized Strategy for Amorphous Pd-Based Nanosheets Boosting Ambient Ammonia Electrosynthesis

The electrocatalytic nitrogen reduction reaction (NRR) is emerging as a great promise for ambient and sustainable NH₃ production while it still suffers from the high adsorption energy of N₂ , the difficulty of *NN protonation, and inevitable hydrogen evolution, leading to a great challenge for efficient NRR. Herein, we synthesized a series of amorphous trimetal Pd-based (PdCoM (M = Cu, Ag, Fe, Mo)) nanosheets (NSs) with an ultrathin 2D structure, which shows high efficiency and robust electrocatalytic nitrogen fixation. Among them, amorphous PdCoCu NSs exhibit excellent NRR activity at low overpotentials with an NH₃ yield of 60.68 µg h^-1 mg_cat ^-1 and a corresponding Faraday efficiency of 42.93% at -0.05 V versus reversible hydrogen electrode as well as outstanding stability with only 5% decrease after a long test period of 40 h at room temperature. The superior NRR activity and robust stability should be attributed to the large specific surface area, abundant active sites as well as structural engineering and electronic effect that boosts up the Pd 4d band center, which further efficiently restrains the hydrogen evolution. This work offers an opportunity for more energy conversion devices through the novel strategy for designing active and stable catalysts.

Advances in the Electrocatalytic Hydrogen Evolution Reaction by Metal Nanoclusters-based Materials

With the development of renewable energy systems, clean hydrogen is burgeoning as an optimal alternative to fossil fuels, in which its application is promising to retarding the global energy and environmental crisis. The hydrogen evolution reaction (HER), capable of producing high-purity hydrogen rapidly in electrocatalytic water splitting, has received much attention. Abundant research about HER has been done, focusing on advanced electrocatalyst design with high efficiency and robust stability. As potential HER catalysts, metal nanoclusters (MNCs) have been studied extensively. They are composed of several to a hundred metal atoms, with sizes being comparable to the Fermi wavelength of electrons, that is, < 2.0 nm. Different from metal atoms/nanoparticles, they exhibit unique catalytic properties due to their quantum size effect and low-coordination environment. In this review, the activity-enhancing approaches of MNCs applied in HER electrocatalysis are mainly summarized. Furthermore, recent progress in MNCs classified with different stabilization strategies, that is, the freestanding MNCs, MNCs with organic, metal and carbon supports, are introduced. Finally, the current challenges and deficiencies of these MNCs for HER are prospected.

Partial deligandation activated ZIF-67 for efficient electrocatalytic oxygen reduction reaction

Removing the blocked molecular groups and fully exposing the intrinsic active sites of metal-organic frameworks (MOFs) could give full play to their advantages of multi-active sites and multi-channel mass transfer, which will benefit the electrocatalytic oxygen reduction reaction (ORR) in fuel cells. Here, the partial diligandation-activated ZIF-67 (named as ZIF-67–400) with excellent ORR performance was obtained by simple low-temperature pyrolysis. The ORR electrocatalytic activity exhibits a half-wave potential of 0.82 V and the stability of maintaining 96% activity after 10 h of operation, which is comparable to commercial Pt/C. Further research studies reveal that the morphology, special dodecahedron configuration, and crystal structure of ZIF-67-400 are maintained well during the pyrolysis, but some hydrocarbon groups in the ligands are eliminated, resulting in the active sites being exposed and coordinated with the intrinsic porosity, improving the catalytic performance. This work may provide an alternative path for activating the electrocatalytic performance of metal-organic frameworks by low-temperature annealing.

Multicomponent Solar Cells with High Fill Factors and Efficiencies Based on Non-Fullerene Acceptor Isomers

Multicomponent organic solar cells (OSCs), such as the ternary and quaternary OSCs, not only inherit the simplicity of binary OSCs but further promote light harvesting and power conversion efficiency (PCE). Here, we propose a new type of multicomponent solar cells with non-fullerene acceptor isomers. Specifically, we fabricate OSCs with the polymer donor J71 and a mixture of isomers, ITCF, as the acceptors. In comparison, the ternary OSC devices with J71 and two structurally similar (not isomeric) NFAs (IT-DM and IT-4F) are made as control. The morphology experiments reveal that the isomers-containing blend film demonstrates increased crystallinity, more ideal domain size, and a more favorable packing orientation compared with the IT-DM/IT-4F ternary blend. The favorable orientation is correlated with the balanced charge transport, increased exciton dissociation and decreased bimolecular recombination in the ITCF-isomer-based blend film, which contributes to the high fill factor (FF), and thus the high PCE. Additionally, to evaluate the generality of this method, we examine other acceptor isomers including IT-M, IXIC-2Cl and SY1, which show same trend as the ITCF isomers. These results demonstrate that using isomeric blends as the acceptor can be a promising approach to promote the performance of multicomponent non-fullerene OSCs.