Ammonia Electrolysis Research Articles

Electrochemical activation of Pt electrode for efficient and stable anion exchange membrane ammonia electrolyzer

Replacing the oxygen evolution reaction in water electrolysis with ammonia oxidation reaction enables low voltage hydrogen production. Pt is a promising catalyst for the ammonia oxidation reaction due to its superior dehydrogenation and low affinity for *N, but Nads poisoning deactivates the Pt surface. This study proposes a method to improve ammonia oxidation performance and stability through electrochemical activation, introducing cathodic corrosion and recovery conditions. The half-cell results showed a peak current density of 74.2 mA cm−2 and retention ratio of 17 %. Adjusting the lower and upper cell voltage in a membrane electrode assembly based single cell optimized surface cleaning and inhibits further poisoning by O/OHads above 0.75 Vcell. Furthermore, incorporation of recovery conditions can enhance the stability of poisoned electrode compared to that in chronoamperometry test. The results of pulsed ammonia electrolysis tests incorporating recovery conditions suggested a novel approach to practical hydrogen production by stabilizing catalysts with a 83 % Faradaic efficiency at 0.1 A cm−2

Energy-efficient and cost-effective ammonia electrolysis for converting ammonia to green hydrogen

Energy-efficient and cost-effective ammonia electrolysis for converting ammonia to green hydrogen

Producing Hydrogen with Less Energy in Ammonia Electrolyzer Stack Using Pt-Ir Catalyst Dual-Layer Electrode

Electrochemical ammonia decomposition has recently been regarded as a possible future technology for CO2-free hydrogen production. Pt-based catalysts have already known for having excellent activity in ammonia oxidation reactions (AOR) due to the fast dehydrogenation step enabled by the moderate adsorption strengths of nitrogen species [1]. Among them, the incorporation of Ir into Pt notably decreases the activation energy required for ammonia oxidation on Pt, lowing onset potential in alkaline media [2]. Besides, the electrolysis of ammonia has a less energy consumption than water electrolysis because of the lower operating voltage at the Anode [3]. In this study, we fabricated dual-layer electrode containing Pt-Ir catalyst, enhancing the AOR catalytic activity and showing long-term stability. The ammonia electrolysis single-cell with an anion exchange membrane (AEM) was successfully operating and then scaled up to a large area stack cell. We observed that this electrolyzer stack cell produced high-purity hydrogen using less energy than water electrolysis.AcknowledgementsThis research was supported by National R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (NRF-2021K1A4A8A01079455). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) [No. 2021R1A5A1028138].Reference[1] J. Liu, Z. Liu, Adv. Funct. Mater 2022, 32, 2110702[2] A. Estejab, G. G. Botte, Comput. Theor. Chem 2016, 1091, 31-40[3] J. Gwak, M. Choun, ChemSusChem 2016, 9, 403–408

Electrocatalytic Ammonia Oxidation to Nitrite and Nitrate with NiOOH‐Ni

AbstractAmmonia electrooxidation in aqueous solutions can be a highly energy‐efficient process in producing nitrate and nitrite while generating hydrogen under ambient conditions. However, the kinetics of this reaction are slow and the role of catalyst in facilitating ammonia electrooxidation is not well understood. In this study, a high‐performance NiOOH‐Ni catalyst is introduced for converting ammonia into nitrite with Faraday efficiency of up to 90.4% and nitrate production rate of 1 mg h−1 cm−2. By employing Operando techniques, the role of NiOOH catalyst is elucidated in the dynamic electrooxidation of ammonia. Density functional theory (DFT) calculations support experimental observations and reveal the mechanism of the electrochemical oxidation of ammonia to nitrite and nitrate. Overall, this research contributes to the development of a cost‐effective and highly efficient catalyst for large‐scale ammonia electrolysis, while shedding light on the underlying mechanism of the NiOOH catalyst in ammonia electrooxidation.

Novel Cu(200)/Ti cathode for the enhancement of N2 selectivity in direct ammonia electrolysis: The controls of Cu cathode facet orientation

Direct electrochemical ammonia oxidation reaction (AOR) using NiCu-based anodes is effective in removing ammonia from wastewater. However, this type of anode frequently produces undesired byproducts NO3−. Here, we investigated three configurations of novel Cu/Ti cathodes (Cu(111)/Ti, Cu(200)/Ti, Cu(220)/Ti) coupled with Cu/Ni foam (Cu/NF) anode to enhance N2 selectivity (SN2) in a direct ammonia electrolysis cell. Cu(200)/Ti cathode improved SN2 from 35 % (bare Ti cathode) to 60 % and it achieved 10–15 % higher SN2 compared to Cu(111)/Ti and Cu(220)/Ti. The improvement of SN2 on Cu(200) facet was ascribed to the high nitrate electroreduction activity and its conversion to N2. In real wastewater, Cu/NF anode-Cu(200)/Ti cathode paired electrolysis system demonstrated its excellent capability of 88 % NH3 removal with 95 % SN2. Our electrolysis system was capable to maintain the residual NH3-N and the NO3-N below 8 mg L−1, meeting effluent discharge standards. Our findings highlighted the importance of the control of Cu cathode facet orientations for an efficient elimination of NO3– and improvement of N2 production during direct ammonia electrolysis.

Recent Advances in Ammonia Electrolysis for Sustainable Hydrogen Generation

Recent Advances in Ammonia Electrolysis for Sustainable Hydrogen Generation

Electrochemical ammonia oxidation on terephthalic acid framework (BDC-NH2) derived core-shell nickel oxide/nickel-enriched 2D carbon nanoflakes (NiO/Ni/CNF)

A terephthalic framework, Ni-BDC-NH2, was used to synthesize the nickel nanoparticles and nanoclusters on-site encapsulated within mesoporous carbon nanoflakes (NiO/Ni/CNF) for ammonia electrolysis. Ni2+ nodes recrystallized to form a core-shell oxide film covering the Ni metal, with the dispersity and particles size influenced by the pyrolysis temperature in a N2 atmosphere. Electrochemical characterization and Raman spectra identified the solid-state Ni(II)⇌Ni(III) transition as the electron mediator, while its lowered onset potential (+1.3 V vs. RHE), compared to that of oxygen evolution reaction (+1.7 V) enhanced the Faradaic efficiency. The performance of electrodes in ammonia oxidation was assessed, which revealed a N2 selectivity of at least 80 % under electrolytic conditions of current density = 0.5 – 1.5 mA cm−2, pH > 10, and initial NH3 level = 50–300 mg-N L−1 using NiO/Ni/CNF(700). An undivided cell equipped with NiO/Ni/CNF(700) anode and Cu/Ni cathode was utilized to treat a real wastewater (∼500 mg-N L−1, pH 4.5). Consequently, both the removal efficiency of NH3 and N2 selectivity surpassed 90 % in a continuous flow mode for 4 days, indicating the durability of electrode system.

Online energy management strategy for ammonia-hydrogen hybrid electric vehicles harnessing deep reinforcement learning

Powertrain electrification and fuel decarbonization play pivotal roles in the pursuit of carbon peak and carbon neutrality within the realm of transportation. Ammonia and hydrogen are essential carbon-neutral fuels suited for deployment in heavy-duty, long-haul transportation applications. The technological complementarity of ammonia and hydrogen can be realized in the current context by combining various energy conversion devices. Energy management strategy (EMS) is one of the critical technologies in hybrid systems. In this study, a novel EMS based on deep reinforcement learning (DRL) is proposed for a heavy-duty automotive hybrid system containing an ammonia-hydrogen internal combustion engine (ICE), a fuel cell system (FCS), an ammonia electrolysis cell (AEC), and Li-ion batteries (LB). To address the protracted training times and convergence challenges intrinsic to DRL, a fuzzy logic control (FLC) is introduced to provide expert demonstrations during the DRL agent's learning process. The incorporation of FLC not only facilitates the convergence speed of the DRL algorithm, but also strikes a good balance between the operation efficiency improvement and battery SOC maintenance. The simulation results show that the proposed EMS improves average efficiency by 2 % with a modest 0.75 % SOC reduction across four operational scenarios compared to the FLC-based EMS. After thorough validation of the proposed EMS, a parametric study is conducted to examine three key parameters: charge mode threshold, FCS power change rate limit, and hybrid mode threshold. The study aims to offer valuable insights for formulating the EMS of the ammonia-hydrogen hybrid system.

Covalent Organic Framework Bifunctional Catalyst for Glucose Oxidation Reaction Coupled Nitrate to Ammonia Electrolysis

Covalent Organic Framework Bifunctional Catalyst for Glucose Oxidation Reaction Coupled Nitrate to Ammonia Electrolysis

100 W-class green hydrogen production from ammonia at a dual-layer electrode containing a Pt-Ir catalyst for an alkaline electrolytic process

Ammonia allows storage and transport of hydrogen over long distances and is an attractive potential hydrogen carrier. Electrochemical decomposition has recently been used for the conversion of ammonia to hydrogen and is regarded as a future technology for production of CO2-free pure hydrogen. Herein, a heterostructural Pt-Ir dual-layer electrode is developed and shown to achieve successful long-term operation in an ammonia electrolyzer with an anion exchange membrane (AEM). This electrolyzer consisted of eight membrane electrode assemblies (MEAs) with a total geometric area of 200 cm2 on the anode side, which resulted in a hydrogen production rate of 25 L h−1. We observed the degradation in MEA performance attributed to changes in the anode catalyst layer during hydrogen production via ammonia electrolysis. Furthermore, we demonstrated the relationship between the ammonia oxidation reaction (AOR) and the oxygen evolution reaction (OER).

Development of a Robust Electrochemical Ammonia Electrolysis Protocol Using in Operando Quantitative Analysis

Ammonia electrolysis is an eco-friendly technology that shows promise for producing clean hydrogen. Compared to water electrolysis, ammonia electrolysis only requires a low external voltage of 0.06 V to produce hydrogen. This research proposes a simple protocol for evaluating the practical properties of electrocatalysts for ammonia electrolysis using in-operando gas chromatography. The protocol allows for reliable and efficient comparison and evaluation of new ammonia oxidation catalysts, including distinguishing between competitive oxidation reactions and monitoring them in real-time. Additionally, the author investigated the correlation between physical or electrochemical surface areas and stability performances to estimate practical stability based on half-cell analysis. The use of this rigorous protocol should aid in evaluating the practical performance of ammonia oxidation and contribute to identifying viable pathways for the practical electrochemical oxidation of ammonia to hydrogen.

(Invited) Ammonia Electrolysis from Fundamentals to Scale up

Dr. Botte’s research group has been studying the ammonia electrolysis process, for the production of nitrogen and hydrogen from ammonia and ammonia waste streams, from fundamentals in materials for electrocatalysis including computational work, mathematical modeling, optimization studies and microkinetic models combined with hydrodynamic analysis, simulation on parallel plates flow cells to system integration and scale-up in a skid with a stack of 6000 cm2 electrolysis cell, the biggest reported in the literature. In this presentation, we will discuss how the integration of the components have been critical for the evolution of the technology. In addition, results from the most recent prototype of this technology, installed in a wastewater treatment plant in line with a clinocliptolite ion exchange system that capture the ammonia from wastewater and concentrated it prior to the inlet of the electrolyzer, will be discussed. The electrochemical process operates in a polarity pulse mode that allows NH3 conversions above 80% with specific energy consumption of 5.7 kWh kg−1 of NH3-N without considering the energy that can be obtained from the H2.

Interface Engineering of PtZn Alloy and Nb2O5 for Promoting Ammonia Oxidation Reaction and Hydrogen Evolution Reaction.

Ammonia electrolysis is a promising technology to obtain green hydrogen with zero-carbon emission, in which ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) occur at the anode and cathode, respectively. However, the lack of efficient catalysts hinders its practical application. Herein, PtZn alloy is combined with Nb2O5 to construct a bifunctional heterostructure catalyst (PtZn-Nb2O5/C). The optimal sample with Nb2O5 content of 7.05 wt % demonstrates the best performance with a peak current density of 304.1 mA mg-1Pt for AOR, and it is only reduced by 17.0% after 4000 cycles of durability tests. For HER, it has a low overpotential of 34 mV at -10 mA cm-2 under the alkaline condition. This can be ascribed to the interfacial interaction between the PtZn alloy and Nb2O5, which adjusts the adsorption behavior of OHad to concurrently promote AOR and HER activity. This work thus proposes a viable strategy to design an efficient bifunctional catalyst for hydrogen generation from ammonia electrolysis.

Economical assessment comparison for hydrogen reconversion from ammonia using thermal decomposition and electrolysis

Ammonia is a promising alternative for the storage and transport of renewable hydrogen over long distances. In this paper, a techno-economic assessment was conducted to evaluate the levelized cost of hydrogen (LCOH) produced from renewable ammonia feedstocks. Both thermal and electrochemical pathways were analyzed. For the thermal pathway we investigated the decomposition using fixed bed reactor and membrane technology, while alkaline electrolysis was studied for the electrochemical route. We evaluated different process scales corresponding to stationary reconversion in a hydrogen refueling station (1000 kgH2/day) or an ammonia import terminal (1500 tNH3/year) and mobile on-board reconversion for a heavy-duty truck (22 kgH2/day). The results show that currently the cheapest option to produce hydrogen from ammonia is the thermal decomposition with membrane technology for import terminal, fixed bed for the hydrogen refueling station, and electrolysis on-board a truck. The levelized cost of hydrogen for the thermal decomposition methods in an ammonia import terminal lie in the range of hydrogen prices produced from today's mix of renewable energy and water as feedstock in Europe. A sensitivity analysis shows that, regardless of the process scale, the parameters with the highest impact on the levelized cost of hydrogen are the reactor temperature for the membrane technology, and ammonia price for fixed bed and electrolysis technologies. The reconversion costs in the latter case are most sensitive to the cell voltage. A future scenario analysis indicates that ammonia electrolysis reconversion costs can be reduced between 14% and 44%, depending on the process scale.

(Invited) Electrocatalytic Ammonia Splitting for Hydrogen Generation

Much of the global effort toward producing solar fuels has involved splitting water to obtain molecular hydrogen. Unfortunately, hydrogen gas has a relatively low energy-per-volume, and extreme cryogenic temperature and pressure is needed to bring hydrogen to a condensed state. An interesting choice for a hydrogen storage medium that circumvents these setbacks is ammonia. Synthesis of ammonia (largely via the Haber-Bosch process) is already the second-largest chemical industrial process in the world, and as a result the infrastructure for ammonia storage and transport already exists. In the first part of this talk, I will introduce a new method of storing liquid ammonia at room temperature and atmospheric pressure by combing it with certain ammonium salts to form binary solutions. Preliminary electrochemical investigations of this interesting solvent system will be introduced, including electrolysis to generate hydrogen and nitrogen. The ammonia oxidation overpotential ultimately limits the efficiency of ammonia electrolysis. The second part of this talk will discuss electrocatalytic measurements of homogeneous electrocatalysts, including the transition metal complex, [Ru(tpy)(dmabpy)NH3]2+ (tpy = 2,2′:6′,2′′-terpyridine, dmabpy = 4,4'-dimethylamino-2,2'-bipyridine), in non-aqueous solvent systems with the aim of lowering the overpotential. Recent results at uncovering the mechanism of ammonia oxidation with this ruthenium catalyst will be presented and used to model and interpret the cyclic voltammetric response of electrocatalysis.

A low-temperature ammonia electrolyser for wastewater treatment and hydrogen production

Ammonia is a pollutant present in wastewater and is also a valuable, carbon-free hydrogen carrier. Stripping, recovery, and anodic oxidation of ammonia to produce hydrogen via electrolysis is gaining momentum as a technology, yet the development of an inexpensive, stable catalytic material is imperative to reduce cost. Here, we report on a new nickel-copper (NiCu) catalyst electrodeposited onto a high surface area nickel felt (NF) as an anode for ammonia electrolysis. Cyclic voltammetry demonstrated that the catalyst/substrate combination reached the highest current density (200 mA cm−2 at 20 °C) achieved for a non-noble metal catalyst. A NiCu/NF electrode was tested in an anion exchange membrane electrolyser for 50 h; it showed good stability and high Faradaic efficiency for ammonia oxidation (88%) and hydrogen production (99%). We demonstrate that this novel electrode catalyst/substrate material combination can oxidise ammonia in a scaled system, and hydrogen can be produced as a valuable by-product at industrial-level current densities and cell voltages lower than that for water electrolysis.

Meticulous integration of N and C active sites in Ni2P electrocatalyst for sustainable ammonia oxidation and efficient hydrogen production

Ammonia, as an efficient hydrogen carrier, is emerging as an alternative energy resource to replace fossil fuels in the carbon–neutral era. Hydrogen production by water electrolysis seeks a lower potential dependent anodic reaction to overcome its energy-inefficiency that originates from the high potential anodic oxygen evolution reaction (OER). In this work, nickel phosphide supported on nitrogen doped-carbon (Ni2P@N-C) was prepared by one-pot synthesis for the bifunctional activity of hydrogen evolution (HER) and ammonia oxidation (AOR) reactions. The Ni2P@N-C electrocatalyst exhibits about 78% decomposition of ammonia compared to the initial concentration. The amount of hydrogen generated in a 0.5 M ammonia environment for 30 min is about 2.144 mmol(H2)/mol(NH3) h cm2. The fabricated ammonia electrolysis cell demonstrates a comparatively low energy consumption rate of 8.611 KWHkg(H2)−1. Thus, engineering a bifunctional electrocatalyst for a low potential anode oxidation reaction and the cathodic HER is a promising strategy to fabricate an energy efficient electrolysis cell for hydrogen production with a low cell potential requirement.

In Situ Study of Hydrogen Permeable Electrodes for Electrolytic Ammonia Synthesis Using Near Ambient Pressure XPS.

Hydrogen permeable electrodes can be utilized for electrolytic ammonia synthesis from dinitrogen, water, and renewable electricity under ambient conditions, providing a promising route toward sustainable ammonia. The understanding of the interactions of adsorbing N and permeating H at the catalytic interface is a critical step toward the optimization of this NH3 synthesis process. In this study, we conducted a unique in situ near ambient pressure X-ray photoelectron spectroscopy experiment to investigate the solid-gas interface of a Ni hydrogen permeable electrode under conditions relevant for ammonia synthesis. Here, we show that the formation of a Ni oxide surface layer blocks the chemisorption of gaseous dinitrogen. However, the Ni 2p and O 1s XPS spectra reveal that electrochemically driven permeating atomic hydrogen effectively reduces the Ni surface at ambient temperature, while H2 does not. Nitrogen gas chemisorbs on the generated metallic sites, followed by hydrogenation via permeating H, as adsorbed N and NH3 are found on the Ni surface. Our findings suggest that the first hydrogenation step to NH and the NH3 desorption might be limiting under the operating conditions. The study was then extended to Fe and Ru surfaces. The formation of surface oxide and nitride species on iron blocks the H permeation and prevents the reaction to advance; while on ruthenium, the stronger Ru-N bond might favor the recombination of permeating hydrogen to H2 over the hydrogenation of adsorbed nitrogen. This work provides insightful results to aid the rational design of efficient electrolytic NH3 synthesis processes based on but not limited to hydrogen permeable electrodes.

Oxygen Vacancy‐Rich La0.5Sr1.5Ni0.9Cu0.1O4–δ as a High‐Performance Bifunctional Catalyst for Symmetric Ammonia Electrolyzer

AbstractIn this study, strontium and copper dual‐doped La2NiO4 annealed in Ar (La0.5Sr1.5Ni0.9Cu0.1O4‐δ‐Ar, LSNC‐Ar) with K2NiF4 structure is strategically designed as an ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) bifunctional catalyst for high‐efficiency ammonia electrolysis. The selective substitution of lanthanum with high content strontium improves the electronic conductivity and increases the oxygen vacancy concentration. Doping of Cu into the B‐site of the perovskite induces a synergistic interplay of Ni and Cu, leading to excellent AOR activity. Due to the excellent AOR and HER activity of doped La2NiO4, a symmetric ammonia electrolyzer based on LSNC‐Ar (SAE‐LSNC‐Ar) is assembled and investigated for the removal of ammonia. In addition, the performance of the SAE is comparable to the ammonia electrolyzer based on a PtIr/C anode and Pt/C cathode at low voltage. This is the first report using an oxide with the K2NiF4 structure as an efficient AOR catalyst. The assembled SAE‐LSNC‐Ar shows ≈95% ammonia removal efficiency in real landfill leachate, which is the highest among electrochemical removal of ammonia in landfill leachate. This study paves an attractive route to explore materials with the K2NiF4 structure as highly efficient AOR/HER bifunctional catalysts for the electrolysis of ammonia.

(Digital Presentation) Electrocatalytic Ammonia Oxidation Coupled with Hydrogen Production - Moving Towards a Carbon Neutral Water Treatment Cycle

Ammonia is a common pollutant, present in municipal wastewater streams. With the continuous shift of people moving to cities and the growing world’s population, the overall wastewater amount is rising. Current ammonia treatment processes in wastewater treatment plants include biological nitrification. Here the ammonia is converted to nitrate or nitrogen. Unfortunately, the capital and operational expenditure costs of such processing are high and the ammonia is converted to products that have no value.Ammonia is a carbon-free energy carrier. Recently, technological solutions have been introduced to strip ammonia from wastewater [1]. The recovered ammonia can be electrochemically oxidised to benign nitrogen in an electrolyser, which can offer a cost-efficient technology to couple wastewater remediation at an anode with the production of a valuable by-product at the cathode, hydrogen. Currently, the commercialisation of the ammonia electrolyser technology is hindered by slow reactions at the anode and the cathode as well as the deactivation or degradation of the catalysts over time [2,3]. Consequently, the development of inexpensive, efficient anode material is imperative to reduce costs associated with ammonia destruction and electrochemical hydrogen production.This study focuses on a non-noble metal NiCu catalyst as a durable anode for alkaline ammonia electrolysis. We report that nickel-copper catalysts can oxidise ammonia to nitrogen at room temperature, see figure below. During electrolysis experiments, gas chromatography of the off-gases confirmed that both, nitrogen at the anode and hydrogen at the cathode, are generated with high faradaic efficiencies. Anode morphology and structure before and after electrolysis was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray Photoelectron Spectroscopy (XPS), and scanning electron microscopy (SEM). To monitor possible intermediates produced by electrolysis, the electrolyte was analysed for NOx regularly by cuvette test and the electrode off-gasses were continuously monitored by GC-TCD. Overall, the electrode showed stability after continuous electrolysis in ammonia for over 30 hours. Further results will be presented at the conference.