It is of great importance to design and develop electrocatalysts that are both long-lasting and efficient for seawater oxidation. Herein, a three-dimensional porous cauliflower-like Ni₃S₂ foam on Ni foam (Ni₃S₂ foam/NF) is proposed as a high-performance electrocatalyst for the oxygen evolution reaction in alkaline seawater. The as-synthesis Ni₃S₂ foam/NF achieves exceptional efficacy, achieving a current density of 100 mA·cm⁻² at mere overpotential of 369 mV. Notably, its electrocatalytic stability extends up to 1000 h at 500 mA·cm⁻².

Seawater electrolysis, especially in coastlines, is widely considered as a sustainable way of making clean and high-purity H₂ from renewable energy; however, the practical viability is challenged severely by the limited anode durability resulting from side reactions of chlorine species. Herein, we report an effective Cl⁻ blocking barrier of NiFe-layer double hydroxide (NiFe-LDH) to harmful chlorine chemistry during alkaline seawater oxidation (ASO), a pre-formed surface-derived NiFe-phosphate (Pi) outer-layer. Specifically, the PO₄³⁻-enriched outer-layer is capable of physically and electrostatically inhibiting Cl⁻ adsorption, which protects active Ni³⁺ sites during ASO. The NiFe-LDH with the NiFe-Pi outer-layer (NiFe-LDH@NiFe-Pi) exhibits higher current densities (j) and lower overpotentials to afford 1 A·cm⁻² (η₁₀₀₀ of 370 mV versus η₁₀₀₀ of 420 mV) than the NiFe-LDH in 1 M KOH + seawater. Notably, the NiFe-LDH@NiFe-Pi also demonstrates longer-term electrochemical durability than NiFe-LDH, attaining 100-h duration at the j of 1 A·cm⁻². Additionally, the importance of surface-derived PO₄³⁻-enriched outer-layer in protecting the active centers, γ-NiOOH, is explained by ex situ characterizations and in situ electrochemical spectroscopic studies.

Advancing efficient and affordable electrocatalysts to boost the oxygen evolution reaction (OER) is pivotal for sustainable green hydrogen production. Herein, we propose the fabrication of nickel-iron alloy nanoparticles-encapsulated on N-doped vertically aligned graphene array on carbon cloth (NiFe@NVG/CC) as a highly active three-dimensional (3D) catalyst electrode for OER. In 1 M KOH, such NiFe@NVG/CC demonstrates outstanding catalytic performance, necessitating merely overpotential of 245 mV for achieving a current density of 10 mA·cm⁻², a remarkably low Tafel slope of 36.2 mV·dec⁻¹. Furthermore, density functional theory calculations validate that the incorporate of N species into graphene can reinforce the electrocatalytic activity though reducing the reaction energy barrier during the conversion of *O to *OOH intermediates. The outstanding performance and structural benefits of NiFe@NVG/CC offer valuable insights for the development of innovative and efficient electrocatalysts for water oxidation.

Nitrate (NO₃⁻), a nitrogen-containing pollutant, is prevalent in aqueous solutions, contributing to a range of environmental and health-related issues. The electrocatalytic reduction of NO₃⁻ holds promise as a sustainable approach to both eliminating NO₃⁻ and generating valuable ammonia (NH₃). Nevertheless, the reduction reaction of NO₃⁻ (NO₃⁻RR), involving 8-electron transfer process, is intricate, necessitating highly efficient electrocatalysts to facilitate the conversion of NO₃⁻ to NH₃. In this study, Fe-doped Co₃O₄ nanowire strutted three-dimensional (3D) pinewood-derived carbon (Fe-Co₃O₄/PC) is proposed as a high-efficiency NO₃⁻RR electrocatalyst for NH₃ production. Operating within 0.1 M NaOH containing NO₃⁻, Fe-Co₃O₄/PC demonstrates exceptional performance, obtain an impressively large NH₃ yield of 0.55 mmol·h⁻¹·cm⁻² and an exceptionally high Faradaic efficiency of 96.5% at −0.5 V, superior to its Co₃O₄/PC counterpart (0.2 mmol·h⁻¹·cm⁻², 73.3%). Furthermore, the study delves into the reaction mechanism of Fe-Co₃O₄ for NO₃⁻RR through theoretical calculations.

Nitrate (NO₃⁻) removal by photochemical-reduction has received extensive attention. However, the low selectivity of NO₃⁻ reduction to N₂ hinders the application of this technology. In this study, a novel Cu@Fe-Cu-CuFe₂O_4−x photocatalyst was prepared by modifying CuFe₂O₄ with KBH₄ and Cu(II), and used to selectively reduce NO₃⁻ to N₂ with a two-step reduction process. In step (1), with Cu@Fe-Cu-CuFe₂O_4−x/ultraviolet (UV) system, 91.0% NO₃⁻ was reduced to 52.3% NO₂⁻ and 39.4% N₂ within 60 min. The rapid removal of NO₃⁻ was due to the synergistic effect of oxygen vacancies, Fe-Cu corrosion cell, and CuFe₂O₄ photocatalysis. In step (2), H₂C₂O₄ and H₂O₂ were introduced into the effluent of step (1) to promote CO₂·⁻ formation via Fe(II) and Fe(III) catalysis and UV radiation, which boosted the selective reduction of NO₂⁻ to N₂. When H₂C₂O₄ and H₂O₂ dosages were both 4.0 mmol·L⁻¹ and the reaction time was 30 min, the removal efficiency of NO₂⁻ achieved 100% and the selectivity of N₂ was 83.0%. Overall, the two-step reduction process achieved 95.0% NO₃⁻ removal efficiency and 90.1% N₂ selectivity with initial NO₃⁻ concentration of 30 mg·N·L⁻¹. In addition, the denitrification mechanism of the two-step reduction process was tentatively proposed.

Seawater electrolysis is an extremely attractive approach for harvesting clean hydrogen energy, but detrimental chlorine species (i.e., chloride and hypochlorite) cause severe corrosion at the anode. Here, we report our recent finding that benzoate anions-intercalated NiFe-layered double hydroxide nanosheet on carbon cloth (BZ-NiFe-LDH/CC) behaves as a highly efficient and durable monolithic catalyst for alkaline seawater oxidation, affords enlarged interlayer spacing of LDH, inhibits chlorine (electro)chemistry, and alleviates local pH drop of the electrode. It only needs an overpotential of 320 mV to reach a current density of 500 mA·cm^–2 in 1 M KOH. In contrast to the fast activity decay of NiFe-LDH/CC counterpart during long-term electrolysis, BZ-NiFe-LDH/CC achieves stable 100-h electrolysis at an industrial-level current density of 500 mA·cm^–2 in alkaline seawater. Operando Raman spectroscopy studies further identify structural changes of disordered δ (Ni^III-O) during the seawater oxidation process.

Seawater electrolysis is the most promising technology for large scale hydrogen production due to the abundance and low cost of seawater in nature. However, compared with the traditional freshwater electrolysis, the issues of electrode poisoning and corrosion will occur during the seawater electrolysis process, and active and stable electrocatalysts for the hydrogen evolution reaction (HER) are thus highly desired. In this work, N, O-doped carbon foam in-situ derived from commercial melamine foam is proposed as a high-active metal-free HER electrocatalyst for seawater splitting. In acidic seawater, our catalyst shows high hydrogen generation performance with small overpotential of 161 mV at 10 mA·cm⁻², a low Tafel slop of 97.5 mV·dec⁻¹, and outstanding stability.

Electrocatalytic nitrate reduction reaction (NO₃⁻RR) emerges as a highly efficient approach toward ammonia synthesis and degrading NO₃⁻ contaminant. In our study, CeO₂ nanoparticles with oxygen vacancies (V_O) decorated N-doped carbon nanorods on graphite paper (CeO_2−x@NC/GP) were demonstrated as a highly efficient NO₃⁻RR electrocatalyst. The CeO_2−x@NC/GP catalyst manifests a significant NH₃ yield up to 712.75 μmol·h⁻¹·cm⁻² at −0.8 V vs. reversible hydrogen electrode (RHE) and remarkable Faradaic efficiency of 92.93% at −0.5 V vs. RHE under alkaline conditions, with excellent durability. Additionally, an assembled Zn-NO₃⁻ battery with CeO_2−x@NC/GP as cathode accomplishes a high-power density of 3.44 mW·cm⁻² and a large NH₃ yield of 145.08 μmol·h⁻¹·cm⁻². Density functional theory results further expose the NO₃⁻ reduction mechanism on CeO₂ (111) surface with V_O.

Ambient electroreduction of nitrogen (N₂) is considered as a green and feasible approach for ammonia (NH₃) synthesis, which urgently demands for efficient electrocatalyst. Morphology has close relationship with catalytic activity of heterogeneous catalysts. Nanoribbon is attractive nanostructure, which possesses the flexibility of one-dimensional nanomaterials, the large surface area of two-dimensional nanomaterials, and lateral size confinement effects. In this work, Cu₃P nanoribbon is proposed as a highly efficient electrocatalyst for N₂-to-NH₃ conversion under benign conditions. When measured in N₂-saturated 0.1 M HCl, such Cu₃P nanoribbon achieves high performance with an excellent Faradaic efficiency as high as 37.8% and a large yield of 18.9 µg·h⁻¹·mg_cat.⁻¹ at −0.2 V. It also demonstrates outstanding stability in long-term electrolysis test at least for 45 h.

To restore the natural nitrogen cycle (N-cycle), artificial N-cycle electrocatalysis with flexibility, sustainability, and compatibility can convert intermittent renewable energy (e.g., wind) to harmful or value-added chemicals with minimal carbon emissions. The background of such N-cycles, such as nitrogen fixation, ammonia oxidation, and nitrate reduction, is briefly introduced here. The discussion of emerging nanostructures in various conversion reactions is focused on the architecture/compositional design, electrochemical performances, reaction mechanisms, and instructive tests. Energy device advancements for achieving more functions as well as in situ/operando characterizations toward understanding key steps are also highlighted. Furthermore, some recently proposed reactions as well as less discussed C–N coupling reactions are also summarized. We classify inorganic nitrogen sources that convert to each other under an applied voltage into three types, namely, abundant nitrogen, toxic nitrate (nitrite), and nitrogen oxides, and useful compounds such as ammonia, hydrazine, and hydroxylamine, with the goal of providing more critical insights into strategies to facilitate the development of our circular nitrogen economy.