In light-emitting electrochemical cells (LECs), the position of the emission zone (EZ) is not predefined via a multilayer architecture design, but governed by a complex motion of electrical and ionic charges. As a result of the evolution of doped charge transport layers that enclose a dynamic intrinsic region until steady state is reached, the EZ is often dynamic during turn-on. For thick sandwich polymer LECs, a continuous change of the emission colour provides a direct visual indication of a moving EZ. Results from an optical and electrical analysis indicate that the intrinsic zone is narrow at early times, but starts to widen during operation, notably well before the electrical device optimum is reached. Results from numerical simulations demonstrate that the only precondition for this event to occur is that the mobilities of anions (μa) and cations (μc) are not equal, and the direction of the EZ shift dictates μc > μa. Quantitative ion profiles reveal that the displacement of ions stops when the intrinsic zone stabilizes, confirming the relation between ion movement and EZ shift. Finally, simulations indicate that the experimental current peak for constant-voltage operation is intrinsic and the subsequent decay does not result from degradation, as commonly stated.

Effects of ion concentration and active layer thickness play a critical role on the performance of light‐emitting electrochemical cells. Expanding on a pioneering materials system comprising the super yellow (SY) polymer and the electrolyte trimethylolpropane ethoxylate (TMPE)/Li+CF3SO3−, it is reported that a slightly lowered salt concentration and layer thickness result in a substantial efficiency increase, and that this increase is confined to a narrow concentration and thickness range. For a film thickness of 70 nm, a blend ratio SY:TMPE:Li+CF3SO3− = 1:0.075:0.0225, and a current of 7.7 mA cm−2 the current efficacy is 11.6 cd A−1, on a par with SY light‐emitting diodes. The optimized salt content can be explained by increased exciton quenching at higher concentrations and hindered carrier injection and conduction at lower concentrations, while the optical dependence on the layer thickness is due to weak microcavity effects. A comprehensive optical modeling study is presented, which includes the doping‐induced changes of the refractive indices and self‐absorption losses due the emission–absorption overlap of intrinsic and doped SY. The analysis indicates either a thickness‐independent emitter position (EP) close to the anode or a thickness‐dependent EP, shifted to the cathode for increased thicknesses.

The redistribution of ions in light-emitting electrochemical cells (LECs) plays a key role in their functionality. The direct quantitative mapping of ion density distributions in operating realistic sandwich-type devices, however, has not been experimentally achieved. Here we operate high-performing [Super Yellow/trimethylolpropane ethoxylate/lithium trifluoromethanesulfonate (Li+CF3SO3 –)] LEC devices inside a time-of-flight secondary ion mass spectrometer and cool the devices after different operation times to liquid nitrogen temperatures before depth profiling is performed. The results reveal the dependence of the elemental and molecular distributions across the device layer on operation conditions. We find that the ion displacements lead to a substantial shift of the local chemical equilibria governing the free ion concentration.

The optimization of the air−solid contactor is critical to improve the efficiency of the direct air capture (DAC) process. To enable comparison of contactors and therefore a step toward optimization, two contactors are prepared in the form of pellets and wash-coated honeycomb monoliths. The desired amine functionalities are successfully incorporated onto these industrially relevant pellets by means of a procedure developed for powders, providing materials with a CO 2 uptake not influenced by the morphology and the structure of the materials according to the sorption measurements. Furthermore, the amine functionalities are incorporated onto alumina wash-coated monoliths that provide a similar CO 2 uptake compared to the pellets. Using breakthrough measurements, dry CO 2 uptakes of 0.44 and 0.4 mmol g sorbent −1 are measured for pellets and for a monolith, respectively. NMR and IR studies of CO 2 uptake show that the CO 2 adsorbs mainly in the form of ammonium carbamate. Both contactors are characterized by estimated Toth isotherm parameters and linear driving force (LDF) coefficients to enable an initial comparison and provide information for further studies of the two contactors. LDF coefficients of 1.5 × 10 −4 and of 1.2 × 10 −3 s −1 are estimated for the pellets and for a monolith, respectively. In comparison to the pellets, the monolith therefore exhibits particularly promising results in terms of adsorption kinetics due to its hierarchical pore structure. This is reflected in the productivity of the adsorption step of 6.48 mol m −3 h −1 for the pellets compared to 7.56 mol m −3 h −1 for the monolith at a pressure drop approximately 1 order of magnitude lower, making the monoliths prime candidates to enhance the efficiency of DAC processes.