Current society is challenged with climate change and aims to adapt and improve to mitigate climate change. This is an extremely challenging transition that requires a paradigm shift from our current fossil fuel driven world to a primarily renewable electricity based one. Increasing the electricity generation alone would not be sufficient, as balance between supply and demand is required. Solar and wind power are intrinsically intermittent with strong diurnal and seasonal variations. 

Therefore, the need arises for electricity storage to compensate for intermittence. Within this thesis we focus on the combined system that can handle both situations, the Ni-Fe alkaline battery and electrolyser. Previously the Ni-Fe battery suffered from limited round-trip efficiency due to hydrogen and oxygen generation. However, when utilized within an integrated electrolysis application, the gas production is intentionally applied for long-term energy storage.
So, within chapter 4, we aimed at improving the Ni electrode by reducing the amount of required nickel, while also improving both electrolyser and battery properties. Depending on the amount of copper substitution, a significant improved electrochemical activity can be obtained. In addition, the Cu doped nickel hydroxide showed stability for over 1000 cycles with the amount of dopant reduced to Ni_0.95Cu_0.05(OH)₂. Overall, this would thus result in requiring 40% less nickel for the same observed capacity.
 
In addition to decarbonizing the electricity production, it is mandatory to replace current industrial processes that require fossil fuel and feedstock with renewable energy and feedstock based alternative processes. Within this Thesis we focused on the oxidation of ammonia to nitrite and nitrate. These products are mainly applied within the synthetic fertilizer production. Ammonia oxidation to nitrites and nitrates is currently performed in the Ostwald process with Pt/Rh gauze. As the ammonia electrooxidation is feasible in ammonia fuel cells, electrochemical oxidation could have potential for replacement of this thermal Ostwald process.
Therefore, in chapter 2, we focus on applying the doped nickel hydroxide materials to increase the performance for ammonia oxidation to nitrate and nitrite. Co, Mn and Cu as dopants showed promising results. Furthermore, it became clear that the reaction was dependent on e Ni(II)/Ni(III) equilibrium as the reaction also occurs through indirect oxidation via the charged NiOOH phase. Under continuous operation at 25 mA/cm² a high faradaic efficiency is obtained with a 97% NO₂^-:NO₃^- selectivity. 

The above sparks interest in further investigation of NiCu_0.2 as promising catalyst in chapter 3, while taking into account the significant of the setup layout. The setup contains a Nafion 117 membrane to keep the counter electrode and nitrite separate, as it would otherwise result in reduction of the nitrite to nitrogen gas or back to ammonia. The Ni_0.8Cu_0.2(OH)₂ can perform ammonia oxidation, with limited oxygen evolution, from 2.5 up to 400 mA/cm². At high initial ammonia concentration of 1 M, more than 75% was able to be converted in 3 hours at this 400 mA/cm² with a faradaic efficiency of 96%. Thus, this work reveals a potential approach for replacing the Ostwald process with electrochemistry within the near future.
... Read more

Electrochemical conversion of ammonia has received increasing attention due to the potential applications for fertiliser production and wastewater treatment. This work demonstrates the application of a homogeneously copper-doped nickel hydroxide, prepared through an easily scalable precipitation method, as an electrochemical oxidation catalyst. A cation exchange membrane divides the cell and prevents re-reduction of the oxidation product. During chronopotentiometry Ni0.8Cu0.2(OH)2 was able to perform ammonia oxidation, with limited oxygen evolution, from 2.5 mA cm−2 up to 400 mA cm−2. The faradaic efficiency for nitrite formation increased with the applied current density. At a high initial ammonia concentration of 1 M, Ni0.8Cu0.2(OH)2 converted 77% of the ammonia in less than 3.5 hours, applying a high current density of 400 mA cm−2. This resulted in a faradaic efficiency of 96% total, which is 91% NO2− and 5% NO3−, which would be impossible in an undivided cell. Therefore, this work demonstrates the potential for efficient and selective ammonia oxidation towards nitrite under industrially relevant current density and conditions. ... Read more

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. ... Read more

The electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the current greenhouse gas emission intensive process to produce ammonia (NH₃) from nitrogen (N₂). However, finding an electrocatalyst that promotes NRR over the competing hydrogen evolution reaction (HER) has proven to be difficult. This difficulty could potentially be addressed by accelerating the electrocatalyst development for NRR by orders of magnitude using high-throughput (HTP) workflows. In this work, we developed a HTP gas diffusion electrode (GDE) cell to screen up to 16 electrocatalysts in parallel. The key innovation of the cell is the use of expanded Polytetrafluoroethylene (ePTFE) gas diffusion layers (GDL) which simplifies the handling of catalyst arrays compared to carbon fabrics and enables sufficient N₂ mass transport. We demonstrate the robustness of the HTP workflow by screening 528 bimetallic catalysts of composition AB (A,B = Ag, Al, Au, Co, Cu, Fe, Mn, Mo, Ni, Pd, Re, Ru, W) for NRR activity. None of the materials produced ammonia significantly over background level which emphasizes the difficulty of finding active electrocatalysts for NRR and narrows down the search space for future studies. ... Read more