SCCER Heat and Electricty Storage Wärme und Strom Speicherung

In the last few years, research to determine the most suitable anode and cathode materials for Na-ion batteries has gained an increased attention. It was a great surprise to discover that pure commercially available elements such as Sb, Sn, or P1-3 can react electrochemically with Na, leading to sustainable reversible capacities as high as 500 mAh/g over more than 100 cycles when carboxymethyl cellulose (CMC) binder is used. These results were unexpected, especially if we compare them to the Li-ion systems. The most commonly used Li-ion binder, polyvinylidene difluoride (PVDF), was reported to not work in the sodium system but no further investigation was done to understand the chemical reasons. Recently, Dahbi et al.4 reported on Na-CMC binder for hard carbon electrodes in Na-ion batteries. They demonstrated better electrochemical results with CMC binder than with PVDF. They also reported that fluoroethylene carbonate (FEC) was essential as an electrolyte additive to improve the cyclability of the PVDF-based electrode.

At present, electricity storage with advanced adiabatic compressed air energy storage (AA-CAES) is considered to the only large-scale alternative to pumped hydro storage. Thermocline storage has gained increasing interest as a solution for thermal energy storage with potentially high efficiency and low costs. The present research aims at enhancing the concept using an experimental-numerical approach to study combined sensible/latent heat storage, which is based on placing a limited amount of steel-encapsulated AlSi₁₂ on top of a packed bed of rocks. The primary motivation for combining sensible and latent heat storage is to reduce the decrease in outflow temperature during discharging of sensible heat storage, which is favorable for downstream applications such as chemical reactions or thermodynamic power cycles. Air is used as heat transfer fluid and the storage may be operated at ambient pressure or at high pressure for the use in AA-CAES.

Single-tank, or thermocline, thermal energy storage (TES) systems, with a packed bed of low cost filler material, represent a valuable alternative to the commonly exploited two-tank solution in nowadays conventional concentrating solar power (CSP) plants. However, an intrinsic drawback of this solution is the decrease of the heat transfer fluid (HTF) outlet temperature, towards the end of the discharge phase, leading to a detrimental effect on the power block efficiency. To avoid the HTF temperature decrease during discharging, a latent heat TES, based on phase change material (PCM), might be exploited instead. However, the high cost of the PCM, along with the relatively low efficiency for large temperature ranges1, are strong limiting factors on the integration of a latent TES into a CSP plant. For this reason, the idea of adding a small amount of encapsulated PCM on top of the packed bed was proposed with the aim of mitigating the HTF temperature decrease during discharging limiting, at the same time, the increment of the overall TES system cost.

Carbon dioxide is a major contributor to global warming and, beyond the mandatory reduction of our emissions, the possibility of recycling this greenhouse gas is becoming increasingly attractive. The electrochemical reduction of CO₂ is an interesting pathway, since a broad range of useful products can be formed such as methanol and formic acid (fuels for PEFC), methane and ethylene (reactants for synthesis or combustion process), CO and H₂ (syngas), etc. [1]. Nevertheless, on top of the high overpotential required to drive this reaction, the electrochemical reduction of CO₂ suffers from a poor yield/selectivity of valuable products [2, 3].Copper-based electrocatalysts seem to be the most efficient to overcome these kinetic and barriers [3], but it has been shown that the size of the Cu (nano)particles envisaged for practical applications can influence the reaction selectivity [4]. In order to clarify this particle size effect, one needs to determine the electrochemically active surface area (ECSA) of the catalysts of interest that, for Cu, can be derived in-situ by lead underpotential deposition (Pb-UPD) [5]. Additionally, the selectivity of the CO₂-reduction reaction on these well-characterized materials needs to be determined with an appropriate technique