Abstract: The Covid era has made us aware of the need for resilient, self-sufficient, and local production. We are likely willing to pay an extra price for that quality. Ammonia (NH3) synthesis accounts for 2 % of global energy production and is an important point of attention for the development of green energy technologies. Therefore, we propose a thermally integrated process for H2 production and NH3 synthesis using plasma technology, and we evaluate its techno-economic performance and CO2 footprint by life cycle assessment (LCA). The key is to integrate energy-wise a high-temperature plasma (HTP) process, with a (low-temperature) non-thermal plasma (NTP) process and to envision their joint economic potential. This particularly means raising the temperature of the NTP process, which is typically below 100 ◦ C, taking advantage of the heat released from the HTP process. For that purpose, we proposed the integrated process and conducted chemical kinetics simulations in the NTP section to determine the thermodynamically feasible operating window of this novel combined plasma process. The results suggest that an NH3 yield of 2.2 mol% can be attained at 302 ◦ C at an energy yield of 1.1 g NH3/kWh. Cost calculations show that the economic performance is far from commercial, mainly because of the too low energy yield of the NTP process. However, when we base our costs on the best literature value and plausible future scenarios for the NTP energy yield, we reach a cost prediction below 452 $/tonne NH3, which is competitive with conventional small-scale Haber-Bosch NH3 synthesis for distributed production. In addition, we demonstrate that biogas can be used as feed, thus allowing the proposed integrated reactor concept to be part of a biogas-to-ammonia circular concept. Moreover, by LCA we demonstrate the environmental benefits of the pro­posed plant, which could cut by half the carbon emissions when supplied by photovoltaic electricity, and even invert the carbon balance when supplied by wind power due to the avoided emissions of the carbon black credits.

Abstract: A new method is developed for synthesizing Ti4O7 supported Ru@Pt core–shell catalyst (Ru@Pt/Ti4O7) through pyrolysis followed by microwave irradiation. The purpose is to improve the Ru durability of PtRu from core–shell structure and strong bonding to Ti4O7 oxide. In this method, the first step is to co-reduce the mixture of ruthenium precursor and TiO2 in a H2 reducing atmosphere under heat-treatment to obtain a Ru core on Ti4O7 support, and the second step is to create a shell of platinum via microwave irradiation. Energy dispersive X-ray spectrometry, X-ray Diffraction, High-resolution Scanning Transmission Electron Microscopy with the high-angle annular dark-field method and Electron Energy-Loss Spectroscopy are used to demonstrate that this catalyst with larger particles has a core–shell structure with a Ru core and a Pt shell. Electrochemical measurements show Ru@Pt/Ti4O7 catalyst has a higher CO-tolerance capability than that of PtRu/C alloy catalyst.

Abstract: Nickel-containing N-doped carbons were synthesized for the electrochemical reduction of CO2 to CO, which is a promising approach to reduce the atmospheric CO2 levels and its negative impact on the environment. Unfortunately, poor performance (activity, selectivity and/or stability) is still a major hurdle for the economical implementation of this type of materials. The electrocatalysts were prepared through an easily up-scalable and easily tunable method based on the pyrolysis of Ni-containing N-doped carbons. Ni–N–AC–B1 synthesized with a high relative amount of nitrogen and nickel with respect to carbon, was identified as the most promising candidate for this reaction based on its partial CO current density (4.2 mA cm−2), its overpotential (0.57 V) and its faradaic efficiency to CO (>99%). This results in unprecedented values for the current density per g active sites (690 A g−1 active sites). Combined with its decent stability and its high performance in an actual electrolyzer setup, this makes it a promising candidate for the electrochemical reduction of CO2 to CO on a larger scale. Finally, the evaluation of this kind of material in a flow-cell setup has been limited and to the best of our knowledge never included an evaluation of several crucial parameters (e.g. electrolyte type, anode composition and membrane type) and is an essential investigation in the move towards up-scaling and ultimately industrial application of this technique. This study resulted in an optimal cell configuration, consisting of Pt as an anode, Fumatech® as the membrane and 1 M KHCO3 and 2 M KOH as catholyte and anolyte, respectively. In conclusion, this research offers a unique combination of electrocatalyst development and reactor optimization.

Abstract: The irreversible release of the lattice oxygen in layered cathodes is one of the major degradation mechanisms of lithium ion batteries, which accounts for a number of battery failures including the voltage/capacity fade, loss of cation ions and detachment of the primary particles, etc. Oxygen release is generally attributed to the stepwise thermodynamic controlled phase transitions from the layered to spinel and rock salt phases. Here, we report a strong kinetic effect from the mobility of cation ions, whose migration barrier can be significantly modulated by the phase epitaxy at the degrading interface. It ends up with a clear oxygen release heterogeneity and completely different reaction pathways between the thin and thick areas, as well as the interparticle valence boundaries, both of which widely exist in the mainstream cathode design with the secondary agglomerates. This work unveils the origin of the heterogenous oxygen release in the layered cathodes. It also sheds light on the rational design of cathode materials with enhanced oxygen stability by suppressing the cation migration.

Abstract: Despite the recent promising potential of plasma-based nitrogen fixation, the technology faces significant challenges in efficient upscaling. To tackle this challenge, we investigate two reactors, i.e., a small one, operating in a flow rate range of 5-20 ln min-1 and current range of 200-500 mA, and a larger one, operating at higher flow rate (100-300 ln min-1) and current (400-1000 mA). Both reactors operate in a pin-to-pin configuration and are powered by direct current (DC) from the same power supply unit, to allow easy comparison and evaluate the effect of upscaling. In the small reactor, we achieve the lowest energy cost (EC) of 2.8 MJ mol-1, for a NOx concentration of 1.72%, at a flow rate of 20 ln min-1, yielding a production rate (PR) of 33 g h-1. These values are obtained in air; in oxygen-enriched air, the results are typically better, at the cost of producing oxygen-enriched air. In the large reactor, the higher flow rates reduce the NOx concentration due to lower SEI, while maintaining a similar EC. This stresses the important effect of the geometrical configuration of the arc, which is typically concentrated in the center of the reactor, resulting in limited coverage of the reacting gas flow, and this is identified as the limiting factor for upscaling. However, our experiments reveal that by changing the reactor configuration, and thus the plasma geometry and power deposition mechanisms, the amount of gas treated by the plasma can be enhanced, leading to successful upscaling. To obtain more insights in our experiments, we performed thermodynamic equilibrium calculations. First of all, they show that our measured lowest EC closely aligns with the calculated minimum thermodynamic equilibrium at atmospheric pressure. In addition, they reveal that the limited NOx production in the large reactor results from the contracted nature of the plasma. To solve this limitation, we let the large reactor operate in so-called torch configuration. Indeed, the latter enhances the NOx concentrations compared to the pin-to-pin configuration, yielding a PR of 80 g h-1 at an EC of 2.9 MJ mol-1 and NOx concentration of 0.31%. This illustrates the importance of reactor design in upscaling. With the focus on feasibility evaluation of scaling-up plasma-based nitrogen fixation by combined experiments and thermodynamic modelling, we aim to tackle the challenge of design and development of an energy-efficient and scaled-up plasma reactor.