Non-precious group metal electrocatalysts are explored for CO2 reduction. Carbon-based metal-nitrogen-carbon (M-N-C) catalysts are investigated and tested via a handmade microfluidic flow cell. Copper-based catalysts are also explored for the reduction of CO2 as so far as how the solvent and acidic/basic moiety dopant content may influence the observed performance. The M-N-C catalysts are explored based on the sacrificial support method (SSM) which was developed by the Atanassov Lab in 2008. A bifunctional bi-metallic M-N-C is developed and studied for syngas production. Finally, a novel synthesis method for M-N-C catalysts is presented which is a one-pot synthesis that produces catalysts with comparable or improved activity for CO2 reduction compared to the state-of-the-art and SSM catalysts. This novel synthesis may be tailored for a range of electrocatalytic applications. As such, it is an industry disrupting technology due to its requiring no harsh solvents of any kind as well its industrial scalability. The materials characterization is explored using standard analytic methods such as transmission electron microscopy (TEM), and X-Ray Diffraction (XRD). The elemental mapping of the catalysts is explored via energy dispersive X-ray spectroscopy (EDS). X-ray Photoelectron spectroscopy (XPS) is used for assessing the surface chemical changes of the catalysts. Scanning electron microscopy (SEM), combined with BET adsorption studies, Raman spectroscopy, and studies of the metal coordination sphere(s) using XANES/NEXAFS are also employed. The electrochemical characterization is carried out using voltametric techniques: linear sweep voltammetry (LSV), cyclic voltammetry (CV), potentiostatic electrochemical impedance spectroscopy (PEIS), and chronoamperometry (CA). The gas-phase product distribution is explored via gas chromatography and the liquid-phase product distribution is assessed by 1H NMR. The material/electrochemical techniques are used in tandem to suggest possible electrocatalytic mechanism and reasons for the observed activity/selectivity. The catalyst development is approached from one of two perspectives: either i.) to gain theoretical and fundamental physical insight to the heterogeneous electrocatalytic process itself or ii.) to assess the possibility for the catalysts to be explored for industrial applications. Addressing the second point, the ease of manufacturability as well as the robustness of the developed catalysts are considered. Finally, a novel Ni-N-C catalyst is developed which shows unmatched selectivity for CO production at both high overpotential and low overpotential. Conventionally and before this catalyst, Ni-N-C was only able to achieve high selectivity at high overpotential. The novel Ni-N-C synthesized here shows > 85 % faradaic efficiency for CO formation (FECO) at -0.3 V vs. RHE and > 99 % FECO at -1.1 V vs. RHE.

Proton Exchange Membrane Fuel Cells or Polymer Electrolyte Membrane Fuel Cells (PEMFCs) is one of the most promising and advancing technology, because of its various advantages such as low temperature operations, quick start-up times and high current and power densities. It has wide range of applications from portable to transportation to stationary applications. But commercialization of this technology is still hindered by several challenges such as cathode catalytic activity and durability.

Homogeneously dispersed platinum nanoparticles over carbon-based supports is the commercial benchmark catalyst at the cathode. However, carbon supports are highly susceptible to corrosion when subjected to high potentials leading to cause major performance losses. Hence corrosion-resistant highly stable support materials are needed. In this study we are exploring highly stable transition metal oxide supports for Pt and Pt-Ni alloy catalysts in PEMFC.

Density functional theory calculations were used to understand the structural, electronic, and stability properties of doped transition metal oxides and to guide the material synthesis. Four different metal oxide (Sb-SnO2, Ru-TiO2, Ta-TiO2, Nb-TiO2) supports were obtained using Sol-Gel and Aerogel-Xerogel methods. Platinum nanoparticles and platinum-nickel alloy nanoparticles were deposited onto a commercial carbon (XC 72R), and metal oxide supports using a microwave-assisted modified polyol method to attain uniform and homogenous Pt nanoparticles dispersion.

All the catalysts were subjected to several physico- chemical and electrochemical characterizations to understand their structural, morphological and electrocatalytic properties towards oxygen reduction reaction at cathode. The surface morphology of these catalysts observed through scanning-transmission electron microscopy (STEM) showed epitaxial growth of Pt nanoparticles onto the support oxides, unlike carbon support.

The oxygen reduction reaction specific activity, investigated in 0.1M HClO4 electrolyte, using rotating disk electrode set-up showed a 5-fold and 2-fold enhancement in the case of Pt/Ru-SnO2, and Pt-Ni/Ru-SnO2 respectively, and a similar performance in case of Pt/Sb-SnO2 compared to Pt/XC 72R because of the strong metal support interactions. The in-situ performance of these catalysts is also investigated in PEMFC.

This dissertation provides an exploration of transition metal oxide supports for Pt and Pt-alloy catalysts, and possible applications of these materials in different fuel cells and electrolyzers.

Decarbonization of energy technologies is crucial for reducing greenhouse gas emissions and their effect on climate change. An increased spotlight has been placed on eliminating emissions stemming from the transportation sector towards zero-carbon energy landscapes. Recent efforts have focused on the deployment of proton exchange membrane fuel cells (PEMFCs) in heavy duty vehicles, which contribute an extremely disproportionally high percentage of CO2 emissions into the atmosphere. This application of PEMFCs, however, requires highly durable oxygen reduction reaction (ORR) catalysts. One significant roadblock is the susceptibility of carbon supports of ORR catalysts towards electrochemical oxidation and corrosion. Hence, major improvements in corrosion-resistant carbon supports are required in order to reach the goal of implementing PEMFCs in heavy duty vehicles.

The interactions between carbon supports and the platinum nanoparticles deposited on them are key towards mitigating ORR catalytic activity losses. Amorphous carbon contains a high density of platinum anchoring sites but is extremely susceptible to oxidation. Graphitic carbon is oxidation-resistant but lacks platinum anchoring sites, which leads to agglomeration of the active material and reduced electrochemical performance. Bulk graphitic content is commonly cited as a measure of a carbon support’s resistance to electrochemical oxidation, yet this value provides little to no insight into the actual morphology of the carbon. Thus, rational design of carbon supports entails thorough understanding of the physical, chemical, and electronic structure of the supports. This dissertation addresses this knowledge gap by probing various novel carbon materials and focusing on the structure-to-property relationships between support morphology and composition and ORR catalytic performance. The specific studies are detailed as follows:

i) Adopting Strategies to Integrate Corrosion-resistant Carbon-based Materials as Supports for Polymer Electrolyte Membrane Fuel Cell Catalysts The mechanism behind electrochemical oxidation of carbon during fuel cell operation and its effect on the cathode catalyst layer morphology and mass transport are summarized. Various strategies to improve oxidation resistance have been presented to inform rational design of carbon supports.

ii) Easily Synthesized Nitrogen-Doped Carbon Nanospheres as Model Supports for Oxygen Reduction Reaction CatalystsA series of monodisperse nitrogen-doped carbon nanosphere supports (NCS1-3) was synthesized through a one-pot process. These were characterized to establish that the differences between the supports were near-surface concentrations of certain nitrogen moieties and minor differences in pore size distribution. A large batch of platinum nanoparticles was then synthesized and decorated onto the NCS supports. Pt/NCS3 exhibited the best Pt dispersion, exhibiting an electrochemically active surface area more than double that of the other catalysts. This enhanced dispersion was attributed to NCS3 having the highest surface concentration of pyridinic-N, lowest surface concentration of amine-N, and moderate microporous surface area.

iii) Novel FCX Carbon Surface Modification with 1-Pyrene Carboxylic AcidCommercial FCX carbons with high degrees of crystallinity were extensively characterized, establishing key differences in specific surface area and pore size distribution. Platinum loss was observed when decorating FCX300 and FCX500 with Pt nanoparticles. 1-pyrene carboxylic acid was then introduced as a support surface modifier to increase the density of Pt anchoring sites while preserving the surface crystallinity of the carbon supports. Electrochemical rotating disk electrode measurements showed that post modification, the 20 wt% Pt/FCX800P catalyst achieved an extremely high ECSA of 169 ± 40 m2/gPt and outperformed Pt/FCX800 with mass activity and specific activity of 166 ± 6 A/gPt and 376 ± 21 μA/cm2Pt at 0.9 V. Thermogravimetric analysis confirmed that the surface modification with 1-pyrene carboxylic acid increased the catalyst Pt loading due to enhanced interactions with the support.

iv) Impregnation of FCX Carbons with Pt and Pt3Co NanoparticlesAn incipient wetness synthesis procedure was implemented to anchor monodisperse Pt nanoparticles uniformly within the interior pore structure of FCX800 By increasing the Pt loading to 40 wt%, a mass activity of 162 ± 23 A/gPt and a specific activity of 255 ± 34 μA/cm2Pt have been achieved at 0.9 V. By modifying the support with 1-pyrene carboxylic acid beforehand, the catalytic performance improved to 201 ± 57 A/gPt and 255 ± 55 μA/cm2Pt at 0.9 V. The synthesis method was extended to Pt3Co nanoparticles. The catalytic activity of this alloyed catalyst was improved ca. 3 times after undergoing a second pyrolysis step to alter the atomic configuration of the nanoparticles. This 20 wt% Pt3Co/FCX800 catalyst exhibited a mass activity of 121 ± 2 A/gPt and a specific activity of 554 ± 23 μA/cm2Pt at 0.9 V.

Carbon dioxide (CO2) is a greenhouse gas that contributes significantly to the warming of the Earth's atmosphere. The greenhouse effect is the process by which the Earth's atmosphere traps solar radiation, keeping the planet warm enough to support life. However, human activities such as the burning of fossil fuels and deforestation have increased the concentration of atmospheric CO2, intensified the greenhouse effect, and led to global warming. This has resulted in rising sea levels, more frequent and severe weather events, and widespread ecological disruption. Therefore, reducing CO2 emissions and remaining CO2 content in the environment is crucial for mitigating the greenhouse effect and ensuring a sustainable and habitable planet for future generations.

CO2 electroreduction is a promising technology that converts CO2 gas into value-added products such as fuels and chemicals using renewable electricity. This technology offers a potential solution to mitigate greenhouse gas emissions while providing an alternative pathway to produce sustainable fuels and chemicals. The electroreduction of CO2 requires the development of efficient and selective electrocatalysts and optimized electrochemical systems. Herein, this dissertation focused on probing the advanced electrocatalysts, optimized electrochemical system, and fundamental mechanism of CO2 electroreduction to value-added products. The following researches have been investigated:

i) Catalytic hybrid electrocatalytic/biocatalytic cascades for carbon dioxide reduction and valorization.A feasible cascade reaction system of hybrid electrocatalysis and biocatalysis has been reviewed and proposed. The electrocatalysts and related cascade reaction pathways are summarized in a descriptive “connectivity map”, identifying the most important reaction pathways.

ii) Robust palladium hydride catalyst for electrocatalytic formate formation with high CO tolerance.A hydrogen-rich Palladium hydride catalyst (PdH0.5/C) derived from a one-step organic solvent synthesis method has been developed. This electrocatalyst showed a 93.1% faradaic efficiency towards formate at -0.4 V (vs. RHE). The working lifetime reached a record of 4 hours, which was ~15 times longer than a commercial Pd catalyst and outperformed all previous Pd-based electrocatalysts for CO2-HCOO- conversion. The high CO tolerance was attributed to the selectivity improvement induced by lattice hydrogen and the weak CO adsorption strength on diverse active sites (i.e., kink, step, and terrace). Isotopic analysis revealed the direct participation of the lattice hydrogen in the protonation of CO2 molecules in formate formation.

iii) Promoting electrolysis of carbon monoxide toward acetate and 1-propanol in flow electrolyzer.Practical approaches for improving acetate and 1-propanol selectivity and yield from CO electrolysis using a commercial copper catalyst have been studied. Acetate showed a strong pH dependence with an optimum performance at 90% Faradaic efficiency and 128 mA cm−2 current density. In addition, 1-propanol showed a strong catalyst-loading dependence, achieving 20% Faradaic efficiency under high-catalyst-loading conditions. In situ Raman and Multiphysics modeling further demonstrated the mechanism of the improvements.

Nitrate reduction reaction in an electrochemical system has recently supplied us with a new pathway to generate ammonia for a post-carbon world. However, the low current density and yield rate as shown in relevant studies limit the NO3RR process. In this thesis, we developed a new catalyst system consisting of γ-Fe2O3 nanoparticles supported on atomically dispersed Fe-N-C. By combining the activity of both the nanoparticles and single atom sites, we were able to achieve an ultrahigh NO3RR activity, with a maximum partial current density of 1.95 A/cm2, a Faradaic efficiency for NH3 of 100%, and an NH3 yield rate of over 9 mmol hr-1 cm-2. Our result of XPS after electrochemical experiments demonstrates the importance of a pre-reduction activation step to generate exposed Fe0 sites from the γ-Fe2O3 (Fe3+) and durability study reveals the robustness of the catalyst, maintaining a current of -1.4 A cm-2, a near unity FENH3 over 24 hours at highly reductive potentials. These findings highlight the potential of active particle-active support systems to enhance NO3RR performance and achieve industrially relevant current densities.

With increasing global energy demand and energy-related carbon emissions, the transportation sector (accounting for over 25% of total greenhouse gas emissions in the United States) must be pushed towards total decarbonization. The polymer electrolyte membrane fuel cells (PEMFC) are a promising energy conversion technology towards the zero-emission goals in transportation applications. However, the high prices and short life cycles of the electrocatalytic materials hinder the widespread commercialization of PEMFCs. Specifically, the design of the cathode catalyst materials (driving the sluggish cathodic oxygen reduction reaction) is instrumental in the success of PEMFCs. Current industry standards utilize a high platinum content catalyst (in nanoparticle form) supported on carbon blacks. The understanding and development of the ideal catalyst layer is three-fold: (1) the nanoparticle-ionomer interface, (2) the nanoparticle-support interface, and (3) the ionomer-support interface. The first portion of my work outlines the ideal cathodic catalyst layer based on a review of recent works which encompasses all three interfacial interactions. The second portion of my work addresses the solid-state integration challenges (i.e., the nanoparticle-ionomer interactions) for the advanced structured Pt-based nanomaterials. The final portion of my work addresses the next generation design parameters of carbon-based supports with a focus on nanoparticle-support interactions.

Metal-air batteries (MAB) is becoming a revived interest because of its high theoretical energy density, low-cost, and environmentally friendly nature. It has wide range of applications from portable transportation to stationary applications. However, commercialization of this technology is hindered by the limitations associated with the metal anode, air cathode, and electrolyte.Commercial benchmark catalysts at the cathode and anode are platinum nanoparticles over carbon-based supports and iridium oxide particles, respectively. However, carbon supports are highly susceptible to corrosion resulting in major performance losses. These metals are also expensive, limited, and difficult to obtain. Hence, corrosion-resistant support materials or an alternative metal are needed. In this study, catalytic activity of a library of transition metal oxides with various supports is explored. All the catalysts were characterized physically and electrochemically to understand their morphological and electrocatalytic properties towards oxygen reduction reaction and oxygen evolution reaction. The oxygen reduction reaction activity, investigated in aqueous 1 M KOH electrolyte, using rotating disk electrode showed worse performance than benchmark Pt/C. However, the oxygen evolution reaction activity surpassed performance of industrial catalyst IrOx. The best performing catalyst in nickel iron oxides and nickel cobalt oxides, neglecting carbon supports, are also investigated in MABs. This thesis provides an exploration of novel bifunctional catalysts tested electrochemically in aqueous 1 M KOH and aqueous 2 M NaCl. The best performing catalysts are then tested in a Zinc-Air battery in aqueous 1 M KOH.

This work investigates the oxygen reduction reaction (ORR) mechanism on Pt nanoparticles (NPs) dispersed on several carbon blacks with various physicochemical properties (i.e. specific surface area ranging from 80 to 900 m2 g-1, different graphitization degree, etc.). Using the kinetic isotope effect (KIE) along with various electrochemical characterizations, it was determined that the rate determining step (RDS) of the ORR is a proton-independent step when the density of Pt NPs on the surface of the carbon support is high. Upon decrease of the density of Pt NPs on the surface, the RDS of the ORR starts involving a proton, as denoted by an increase of the KIE > 1. This underlined the critical role played by the carbon support in the oxygen reduction reaction electrocatalysis by Pt supported on high surface area carbon. Furthermore, two of these carbon supports were selected and using the same synthesis methods, different loadings of Pt NPs were deposited on them. This allowed us to investigate the effect of catalyst loading, thus, take another approach to assess the particle proximity effect on the ORR. The durability and performance of the selected electrocatalysts were also explored in a membrane electrode assembly (MEA) in real-world operational conditions of automotive fuel cells. The effect of the loading of the platinum nanoparticles (Pt NPs) supported on two of the carbon supports with different morphologies (93 vs. 890 m2 g-1) on the oxygen reduction reaction (ORR) was also investigated. The correlation between their electrochemical performances with their physico-chemical properties was suggested. The experiments were extended from bench-scale lab tests to pilot-size membrane electrode assembly (MEA) fuel cell testing where the performance and durability of the in-house synthesized electrocatalyst was investigated. On the result basis, it was confirmed that low platinum loading on a high surface area carbon support resulted in a contribution of the latter to the ORR (see Chapter II for additional details). Moreover, it was observed that in the MEA systems, when using electrocatalyst with a large loading of Pt on the electrode – and thus a thin catalytic layer on the cathode side – at high current densities, flooding would partially block the Pt active site and thus limits the fuel cell performances. Finally, the heterogeneity of polymer electrolyte fuel cells (PEFCs) catalyst degradation was studied under varied relative humidity and type of feed gas. Accelerated stress tests (AST) were performed on four membrane electrode assemblies (MEAs) under wet and dry conditions in air or nitrogen environment for 30,000 square cycles from 0.60 V to 0.95 V (or open circuit voltage (OCV) for air since during cycling in air the OCV drops to values below 0.9 V). It was observed that the largest electrochemical active area (ECSA) loss during the ASTs was for MEA in wet conditions under nitrogen gas. This was mainly attributed to higher upper potential limit (UPL) of 0.95 V that was maintained during experiment and to higher water content in the MEA enabling higher Pt2+ mobility. In air the OCV was lower than 0.95 V during cycling reducing the overall upper potential limit (UPL) to below 0.95 V and thus reducing the rate of platinum oxide (PtO) formation and dissolution. Micro XRD was performed on end of life (EOL) MEAs to show Pt particle size distribution under lands and channels and in various MEA locations. Largest Pt sizes were observed for wet conditions and under the lands. Both represent locations in MEAs with higher water content. AST in air and wet environment showed the highest Pt particle size growth from inlet to outlet, which is due to larger water content at the outlet compared to the inlet. Micro XRF shows that Pt redistribution is a local phenomenon and Pt loading remains relatively uniform within the MEA. Additional diagnostics were used to understand morphology of the MEA at the EOL and confirmed that catalyst layer support structure does not change during AST. Conclusively, the ORR mechanism is subject to different environmental factors, including the morphological and surface characterization of the carbon support, density of the Pt NPs deposited on the support and operation conditions. A wide range of characterization methods and investigations protocols and procedures, ranging from bench-size lab scale tests to pilot-size automotive operation condition fuel cells was implemented. We hypothesized the ORR mechanism, investigated the effect of surface density and particle proximity of Pt NPs and showed the heterogeneity in the MEAs degradation processes.

Electrification, especially in transportation, is key to objectives mitigating climate change effects. Metal-air batteries, including aluminum-air batteries (AAB), may offer performance and safety improvements over lithium-air batteries by using widely available, inexpensive materials.AAB cell advantages in weight, cost, and safety are countered by high polarization from a persistent oxide film, and by high corrosion rates, most notably in alkaline electrolytes. Much research on these topics has employed pure aluminum or specially prepared alloys to minimize corrosion during experimental evaluation. A key question - could commercial aluminum alloys be used in AAB cells in the immediate future? Thus, twin purposes of this study were to assess the state of current technologies of aluminum-air batteries, and to characterize several commercial aluminum alloys to gauge their suitability for use with common aqueous electrolytes in AAB cells. A comprehensive review of prior AAB works was conducted, including assessments of several other metal-air technologies where common elements, such as catalysts for the oxygen reduction reaction (ORR), are relevant. Effects of anode material composition, and of electrolyte additions as corrosion inhibitors, were considered. Characterization of Al alloy 6061 in alkaline electrolyte was done by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy. The cathodic effect of second-phase intermetallic particles in Al 6061 to spur galvanic corrosion nearly negated inhibitor benefit in 4M sodium hydroxide electrolyte. Detailed experimental studies were conducted in neutral and acidic aqueous electrolytes. Aluminum alloys 4047 (silicon), 6061 (magnesium/silicon), and 7075 (zinc/copper) were evaluated by half-cell electrochemical techniques, and by use in a flow battery cell coupled to platinum-cobalt or iron-nitrogen-carbon catalysts in air-breathing or oxygen-breathing gas diffusion electrodes (GDE). Post-discharge characterization of anode surfaces was done using scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. Each alloy manifested different performance, but the strongest influence on cell performance came from ORR kinetics in the GDE. Cell outputs and aluminum utilizations for all materials were similar, regardless of composition. Given the state of the art in ORR catalysts, this work indicates that there appears to be no impediment to using commercial alloys as anode materials in AAB systems at this time.

Ammonia (NH3) is a critically important molecule, necessary to produce fertilizers and is also used in a variety of household chemical and as a precursor in pharmaceuticals. Additionally, NH3 has a relatively large energy density and can be liquified at mild conditions, making it appealing as not only a chemical feedstock but also as an energy storage vector. Unfortunately, the now century old Haber Bosch (HB) process remains the only way to produce NH3 on a large scale. The HB process is one of the most energy intensive and carbon dioxide emitting processes and is therefore essential to decarbonize as we transition into a greener future. The electrochemical transformation of reactive nitrogen-species is a promising, carbon neutral pathway for NH3 synthesis. Typical approaches utilize di-nitrogen (N2) as a reactant; however, the success of these systems remains unproven. Utilizing a more oxidized form of nitrogen, nitrate (NO3-), presents several advantages such as increased solubility in aqueous electrolytes and favorable adsorption energies, helping to increase the NO3- to NH3 selectivity. The electrochemical nitrate reduction reaction (NO3RR) is a complex 8e- transfer reaction, where the reaction pathway and participation of reaction intermediates is largely unknown. This dissertation addresses these issues by fundamental studies partitioning the reaction pathway over distinct catalytic sites in a bi-metallic system. Then moving to develop a series of physically relevant NO3/NO2RR activity descriptors. Finally, the knowledge gained from the fundamental studies is applied to create an active particle-active support catalyst system, achieving the NO3RR to NH3 at industrial current densities. Specifically, the studies are outlined below. i) Highly durable and selective Fe-and Mo-based atomically dispersed electrocatalysts for nitrate reduction to ammonia via distinct and synergized NO2–pathways An atomically dispersed bi-metallic FeMo-N-C catalyst was developed and was shown computationally and experimentally that the Fe-Nx sites favor NO2- to NH3 conversion, while the Mo-Nx sites favor NO3- to NO2- conversion. These sites were synergized to achieve a NO3- to NH3 efficiency of 94%. Additionally, DFT uniquely demonstrated that over highly oxyphilic sites, such as Mo-Nx the real active site during the reaction is *O-Mo-Nx and can simultaneously adsorb multiple intermediates.

ii) Elucidating electrochemical nitrate and nitrite reduction over atomically dispersed transition metal sitesA library of 3d, 4d, 5d and f-metal atomically dispersed Metal-Nitrogen-Carbon catalysts were synthesized and extensively characterized for their atomically dispersed nature and M-Nx coordination. Electrochemical NO3RR and NO2RR were performed to obtain experimental activity descriptors. DFT was used to generate a series of computational activity descriptors. The experimental and computational activity descriptors were correlated to develop a set of physically relevant computational descriptors, such that the NO3/NO2RR activity of M-N-C catalysts could be accurately predicted with a simple descriptor. Additionally, isotopic doping experiments revealed the complex NO2- production consumption mechanism over the M-N-C catalysts, confirming the 2e- + 6e- transfer pathway rather than the commonly assumed direct 8e- pathway.

iii) Synergizing γ-Fe2O3 nanoparticles on single atom Fe-N-C for nitrate reduction to ammonia at industrial current densities An active particle-active support catalyst system was synthesized by reducing γ-Fe2O3 nanoparticles onto an atomically dispersed Fe-N-C support. The catalyst system was characterized electrochemically to demonstrate the increase in NO3RR performance of the γ-Fe2O3/Fe-N-C system over a γ-Fe2O3/XC72 system. Uniquely, the γ-Fe2O3/Fe-N-C system showed potential independent behavior on the FENH3, allowing for a reductive potential up to -1.2 V vs. RHE, while maintaining a 100% FENH3 and a high YieldNH3 over 9 mmol hr-1 cm-2. An economic analysis invesitagting the levelized cost of NH3 revealed it is more beneficial to reduce the levelized cost of NH3 to operate at a higher over potential of -1.0V at a lower energy efficiency, with a very high NH3 partial current density (1.3 A/cm2). Post-mortem XPS revealed that during the pre-reduction activation step, a surface layer of Fe2+/Fe0 is formed, resulting in the ultra-high NO3RR activity observed.