The electrochemical N 2 reduction reaction has attracted interest as a potential alternative to the Haber−Bosch process, but a significantly low conversion efficiency and a significantly low ammonia production rate stimulate the need for alternatives. Here, we represent the electrochemical reduction of nitric oxide (NO) on a nanostructured Ag electrode in combination with a rationally designed electrolyte containing the EDTA−Fe 2+ metal complex (EFeMC), which results in an ∼100% efficiency for NH 3 with a current density of 50 mA/cm 2 at −0.165 V RHE , without any degradation in catalytic activity or product selectivity up to 120 h. Economic analysis using itemized cost estimation predicted that the synthesis of ammonia from NO reduction in an EFeMC-designed electrolyte can be market competitive at an electricity price of $0.03 kWh −1 with a current density of >125 mA/cm 2 . Therefore, this approach opens an entirely new avenue of renewable electricitydriven ammonia synthesis.

Atomically dispersed precious metal catalysts have emerged as a frontier in catalysis. However, a robust, generic synthetic strategy toward atomically dispersed catalysts is still lacking, which has limited systematic studies revealing their general catalytic trends distinct from those of conventional nanoparticle (NP)-based catalysts. Herein, we report a general synthetic strategy toward atomically dispersed precious metal catalysts, which consists of "trapping" precious metal precursors on a heteroatom-doped carbonaceous layer coated on a carbon support and "immobilizing" them with a SiO 2 layer during thermal activation. Through the "trapping-and-immobilizing" method, five atomically dispersed precious metal catalysts (Os, Ru, Rh, Ir, and Pt) could be obtained and served as model catalysts for unravelling catalytic trends for the oxygen reduction reaction (ORR). Owing to their isolated geometry, the atomically dispersed precious metal catalysts generally showed higher selectivity for H 2 O 2 production than their NP counterparts for the ORR. Among the atomically dispersed catalysts, the H 2 O 2 selectivity was changed by the types of metals, with atomically dispersed Pt catalyst showing the highest selectivity. A combination of experimental results and density functional theory calculations revealed that the selectivity trend of atomically dispersed catalysts could be correlated to the binding energy difference between *OOH and *O species. In terms of 2 e − ORR activity, the atomically dispersed Rh catalyst showed the best activity. Our general approach to atomically dispersed precious metal catalysts may help in understanding their unique catalytic behaviors for the ORR.

Electrocatalytic conversion of CO2 into value-added products offers a new paradigm for a sustainable carbon economy. For active CO2 electrolysis, the single-atom Ni catalyst has been proposed as promising from experiments, but an idealized Ni–N4 site shows an unfavorable energetics from theory, leading to many debates on the chemical nature responsible for high activity. To resolve this conundrum, here we investigated CO2 electrolysis of Ni sites with well-defined coordination, tetraphenylporphyrin (N4–TPP) and 21-oxatetraphenylporphyrin (N3O–TPP). Advanced spectroscopic and computational studies revealed that the broken ligand-field symmetry is the key for active CO2 electrolysis, which subordinates an increase in the Ni redox potential yielding NiI. Along with their importance in activity, ligand-field symmetry and strength are directly related to the stability of the Ni center. This suggests the next quest for an activity–stability map in the domain of ligand-field strength, toward a rational ligand-field engineering of single-atom Ni catalysts for efficient CO2 electrolysis.

Atomically dispersed nickel sites complexed on nitrogen-doped carbon (Ni–N/C) have demonstrated considerable activity for the selective electrochemical carbon dioxide reduction reaction (CO2RR) to CO. However, the high-temperature treatment typically involved during the activation of Ni–N/C catalysts makes the origin of the high activity elusive. In this work, Ni­(II) phthalocyanine molecules grafted on carbon nanotube (NiPc/CNT) and heat-treated NiPc/CNT (H-NiPc/CNT) are exploited as model catalysts to investigate the impact of thermal activation on the structure of active sites and CO2RR activity. H-NiPc/CNT exhibits a ∼4.7-fold higher turnover frequency for CO2RR to CO in comparison to NiPc/CNT. Extended X-ray absorption fine structure analysis and density functional theory (DFT) calculations reveal that the heat treatment transforms the molecular Ni2+–N4 sites of NiPc into Ni+–N3V (V: vacancy) and Ni+–N3 sites incorporated in the graphene lattice that concomitantly involves breakage of Ni–N bonding, shrinkage in the Ni–N–C local structure, and decrease in the oxidation state of the Ni center from +2 to +1. DFT calculations combined with microkinetic modeling suggest that the Ni–N3V site appears to be responsible for the high CO2RR activity because of its lower barrier for the formation of *COOH intermediate and optimum *CO binding energy. In situ/operando X-ray absorption spectroscopy analyses further corroborate the importance of reduced Ni+ species in boosting the CO2RR activity.

An effective lattice engineering method to simultaneously control the defect structure and the porosity of layered double hydroxides (LDHs) was developed by adjusting the elastic deformation and chemical interactions of the nanosheets during the restacking process. The enlargement of the intercalant size and the lowering of the charge density were effective in increasing the content of oxygen vacancies and enhancing the porosity of the stacked nanosheets via layer thinning. The defect-rich Co−Al-LDH−NO 3 − nanohybrid with a small stacking number exhibited excellent performance as an oxygen evolution electrocatalyst and supercapacitor electrode with a large specific capacitance of ∼2230 F g −1 at 1 A g −1 , which is the largest capacitance of carbon-free LDH-based electrodes reported to date. Combined with the results of density functional theory calculations, the observed excellent correlations between the overpotential/capacitance and the defect content/stacking number highlight the importance of defect/stacking structures in optimizing the energy functionalities. This was attributed to enhanced orbital interactions with water/hydroxide at an increased number of defect sites. The present cost-effective lattice engineering process can therefore provide an economically feasible methodology to explore high-performance electrocatalyst/electrode materials.

Rational control of the coordination environment of atomically dispersed catalysts is pivotal to achieve desirable catalytic reactivity. We report the reversible control of coordination structure in atomically dispersed electrocatalysts via ligand exchange reactions to reversibly modulate their reactivity for oxygen reduction reaction (ORR). The CO‐ligated atomically dispersed Rh catalyst exhibited ca. 30‐fold higher ORR activity than the NHx‐ligated catalyst, whereas the latter showed three times higher H2O2 selectivity than the former. Post‐treatments of the catalysts with CO or NH3 allowed the reversible exchange of CO and NHx ligands, which reversibly tuned oxidation state of metal centers and their ORR activity and selectivity. DFT calculations revealed that more reduced oxidation state of CO‐ligated Rh site could further stabilize the *OOH intermediate, facilitating the two‐ and four‐electron pathway ORR. The reversible ligand exchange reactions were generalized to Ir‐ and Pt‐based catalysts.

Alloying is one of the powerful methods to exceed the intrinsic properties of pure metals; however, it is challenging to understand the exact alloying effect without altering other parameters, such as crystal structure. In this study, we chose iron and nickel phosphides as model catalysts for the hydrogen evolution reaction (HER) to elucidate the alloying effect of Fe x Ni2–x P (x = 0.5, 1.0, and 1.5), which has the same P6̅2m crystal structure with different alloy compositions. The Fe0.5Ni1.5P catalyst recorded the optimal HER performances, including small overpotential (0.163 V at 50 mA cm–2), low Tafel slope (65 mV dec–1), and high exchange current density (0.37 mA cm–2), which were superior to pure Ni2P, Fe2P, and other Fe x Ni2–x P catalysts in acidic media. The charge of phosphorus atoms in Fe0.5Ni1.5P was proven the most deficient one by X-ray photoelectron spectroscopy (XPS). The extended X-ray absorption fine structure (EXAFS) data supported that the small distortion degree of the metal–metal (M–M) bonds in the Fe0.5Ni1.5P significantly suppresses the metal to phosphorus (M-to-P) charge transfer and increases the electronic deficiency of phosphorus atoms. We also performed the density functional theory (DFT) calculation to support our charge trend of phosphorus and local distortion of M-to-P bonds. Our finding provided the observation of electron-deficient phosphorus sites modulated by the alloy composition of Fe x Ni2–x P and showed how the degree of the M–M bond distortion correlates with HER properties in acidic media.

Many studies have focused on atomically dispersed metal-nitrogen-carbon (Me–N–C) catalysts owing to their unique chemistry and high catalytic activities. Me–N–C catalysts have active centers resembling metalloporphyrins; thus, being heterogeneous analogs...