Mechanical stability and interfacial stability are the main issues hindering the development of sulphide-based solid state batteries. We review here the recent advances in this field including the alternative of hybrid solid electrolytes.

The encouraging selectivity of copper oxides for the electroreduction of CO2 into ethylene and alcohols has led to a vivid debate on the possible relation between their operando (sub‐)surface oxidation state (i. e. fully reduced or partially oxidized) and this distinct reactivity. The high roughness of the Cu oxides used in previous studies on this matter adds complexity to this controversy and motivated us to prepare quasi‐planar Cu2O thin films that displayed a CO2 reduction selectivity similar to that of oxide‐derived copper catalysts reported in previous studies. Most importantly, when the post‐mortem thin films were transferred for characterization in an air‐free environment, X‐ray photoelectron spectroscopy measurements confirmed their complete reduction in the course of the CO2 reduction reaction. Thus, our results indicate that the selectivity of the Cu oxides featured in previous studies stems from their enhanced roughness, highlighting the importance of controlled sample transfer upon post‐mortem characterization with ex situ techniques.

Solid-state batteries are seen as a possible revolutionary technology, with increased safety and energy density compared to their liquid-electrolyte-based counterparts. Composite polymer/ceramic electrolytes are candidates of interest to develop a reliable solid-state battery due to the potential synergy between the organic (softness ensuring good interfaces) and inorganic (high ionic transport) material properties. Multilayers made of a polymer/ceramic/polymer assembly are model composite electrolytes to investigate ionic charge transport and transfer. Here, multilayer systems are thoroughly studied by electrochemical impedance spectroscopy (EIS) using poly(ethylene oxide) (PEO)-based polymer electrolytes and a NaSICON-based ceramic electrolyte. The EIS methodology allows the decomposition of the total polarization resistance ( R p ) of the multilayer cell as being the sum of bulk electrolyte (migration, R el ), interfacial charge transfer ( R ct ), and diffusion resistance ( R dif ), i.e., R p = R el + R ct + R dif . The phenomena associated with R el , R ct , and R dif are well decoupled in frequencies, and none of the contributions is blocking for ionic transport. In addition, straightforward models to deduce R el , R dif , and t + (cationic transference number) of the multilayer based on the transport properties of the polymer and ceramic electrolytes are proposed. A kinetic model based on the Butler–Volmer framework is also presented to model R ct and its dependency with the polymer electrolyte salt concentration ( C Li + ). Interestingly, the polymer/ceramic interfacial capacitance is found to be independent of C Li + .