Ammonia (NH₃) is a versatile chemical, critical to agriculture and various industries. Today, ammonia is further regarded as one of the most promising carbon-free energy carriers in the net-zero hydrogen economy. Traditionally, the energy-intensive Haber–Bosch process has been mainly used for producing ammonia by the thermocatalytic conversion of high-purity nitrogen and hydrogen, while also contributing to major greenhouse gas emissions due to dependence on fossil fuels. The electrochemical nitrogen reduction reaction (e-NRR) is a highly promising and attractive alternative roadmap to achieving clean and sustainable ammonia production under conditions that are sufficiently mild to be fully powered by renewable energy sources. However, the industrial adoption of e-NRR is currently hindered by its low ammonia yields and poor selectivity resulting from the limited reactivity of nitrogen molecules and the competitive hydrogen evolution reaction (HER) in aqueous electrolyte, respectively. To overcome these barriers, the development of efficient electrocatalysts for e-NRR is essential to the actual realization of this emerging ammonia production technology. Among various types of promising materials, earth-abundant Fe element presents a competitive edge for developing high-performance electrocatalytic N₂ reduction systems owing to its intrinsic activity, low cost, and ease of modification with other elements to form compounds with distinguished catalytic activity. Therefore, this review focuses on recent developments in Fe-based nanomaterials for ammonia synthesis through e-NRR. A detailed overview of the chemistry of e-NRR, its fundamentals, mechanisms, and experimental procedures is given, along with ammonia detection methods and catalyst evaluation metrics. The main part of this review explored various kinds of Fe-based catalysts encompassing the oxides, hydroxides, bimetallic catalysts, single atom catalysts (SACs), metal–organic frameworks (MOFs), and chalcogenides. The analysis and discussion revolved around key traits of the catalysts, including synthesis protocol, structural features, surface properties, and their correlation to catalytic activity based on experimental data and theoretical insights. Additionally, prevailing challenges and opportunities for further advancement of Fe-based e-NRR catalysts are provided.

As global energy demand continues to rise with fossil fuels dwindling at a faster rate, posing energy and environmental concerns, there is a growing interest in exploring alternative, green, and renewable energy sources. Ammonia is a key hydrogen energy carrier and precursor to many value-added products, and the efforts for its generation at commercial scale using greener methods are intensifying to mitigate the reliance on the energy-intensive Haber-Bosch process. The electrochemical nitrogen reduction reaction (e-NRR) is a highly promising way of synthesizing ammonia under energy-efficient, green, and ambient conditions. Despite its attractive potential, the activity and efficiency of conventional e-NRR catalysts are still a major concern due to low selectivity and poor ammonia yields. Inspired by the FeFe and FeV cofactors present in nitrogenases, this study reports the synthesis and electrocatalytic evaluation of FeVO₄ catalyst for N₂ reduction. The FeVO₄ nanoparticles anchored on Fe foam (FF) could serve as an efficient electrocatalyst for the electrochemical nitrogen fixation, achieving a significant performance with highest NH₃ yield of 22.5 µg·h^–1·mg^–1 and Faradaic efficiency (FE) of 20.74% at –0.2 V_RHE in 0.1 M Na₂SO₄. The FeVO₄ electrocatalyst exhibited robust electrochemical stability for 24 h of operation at –0.2 V_RHE. The high catalytic performance originated from the synergistic interactions between Fe and V which serve as dual electron donation centers for effective e-NRR. Furthermore, the coupling interaction between FeVO₄ and FF support exposed abundant intrinsic active sites and facilitated beneficial charge transfer further inducing superior e-NRR activity. Density functional theory (DFT) computations disclosed that surface Fe atoms are the main active centers for e-NRR which proceed via the alternating pathway.

Transition metal based bimetallic oxides are good candidates for electrocatalytic oxygen evolution owing to their variable oxidation states, synergistic effects, good conductivity, convincing electrochemical stability, and low cost. However, these materials are highly susceptible to corrosion during saline seawater electrolysis. This work, for the first time, highlights the role of cerium (Ce) doping in bimetallic strontium cobalt oxide (SrCoO_x) electrocatalyst for electrochemically stable and corrosion-resistant oxygen evolution reaction (OER) in simulated saline water. The experimental results reveal that 0.5% Ce-doped 5% SrCoO_x has the best corrosion resistant ability with respect to the undoped SrCoO_x and various other Ce-doped samples. The growth of CeO₂ nanoparticles and the generation of CeO_x passivation layer through Ce doping were supposed to block the corrosive ions on the surface, thereby hindering chlorine evolution reaction (CER). The Ce³⁺ ions doped inside the SrCoO_x lattice created multiple defects and vacancies which sacrificially facilitate the OER while mitigating the CER. The suppression of corrosive reactions was indicated through low corrosion current (−1.10 μA·cm⁻²) and high corrosion potential (0.90 V vs. RHE) values suggesting slowest corrosion rate and least tendency towards CER in 0.5% Ce-doped 5% SrCoO_x. Consequently, it demonstrated the least Tafel slope of 81.7 mV·dec⁻¹ in saline OER electrolysis with respect to the 121.0 mV·dec⁻¹ was obtained for undoped 5% SrCoO_x. Moreover, the electrochemical stability demonstrated in chronoamperometric OER for 45 h and the cyclic voltammetry (500 cycles) confirmed that 0.5% Ce-doped SrCoO_x electrocatalyst possesses enhanced anticorrosive properties, which was further supported by post-use linear sweep voltammetry, cyclic voltammetry, and X-ray diffraction analyses. Linear polarization resistance study was also employed on the seawater sample, collected locally, to assess the validity of the present work in real marine systems. In view of the observed results, this work can open an alternate pathway to investigate various transition metal oxide systems as potential corrosion resistant electrocatalysts for seawater.

Single-atom catalysts (SACs) have received significant interest for optimizing metal atom utilization and superior catalytic performance in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this study, we investigate a range of single-transition metal (STM₁ = Sc₁, Ti₁, V₁, Cr₁, Mn₁, Fe₁, Co₁, Ni₁, Cu₁, Zr₁, Nb₁, Mo₁, Ru₁, Rh₁, Pd₁, Ag₁, W₁, Re₁, Os₁, Ir₁, Pt₁, and Au₁) atoms supported on graphyne (GY) surface for HER/OER and ORR using first-principle calculations. Ab initio molecular dynamics (AIMD) simulations and phonon dispersion spectra reveal the dynamic and thermal stabilities of the GY surface. The exceptional stability of all supported STM₁ atoms within the H1 cavity of the GY surface exists in an isolated form, facilitating the uniform distribution and proper arrangement of single atoms on GY. In particular, Sc₁, Co₁, Fe₁, and Au₁/GY demonstrate promising catalytic efficiency in the HER due to idealistic ΔG_H* values via the Volmer-Heyrovsky pathway. Notably, Sc₁ and Au₁/GY exhibit superior HER catalytic activity compared to other studied catalysts. Co₁/GY catalyst exhibits higher selectivity and activity for the OER, with an overpotential (0.46 V) comparable to MoC₂, IrO₂, and RuO₂. Also, Rh₁ and Co₁/GY SACs exhibited promising electrocatalysts for the ORR, with an overpotential of 0.36 and 0.46 V, respectively. Therefore, Co₁/GY is a versatile electrocatalyst for metal-air batteries and water-splitting. This study further incorporates computational analysis of the kinetic potential energy barriers of Co₁ and Rh₁ in the OER and ORR. A strong correlation is found between the estimated kinetic activation barriers for the thermodynamic outcomes and all proton-coupled electron transfer steps. We establish a relation for the Gibbs free energy of intermediates to understand the mechanism of SACs supported on STM₁/GY and introduce a key descriptor. This study highlights GY as a favorable single-atom support for designing highly active and cost-effective versatile electrocatalysts for practical applications.