Immobilization of Polyiodide Redox Species in Porous Carbon for Battery-Like Electrodes in Eco-Friendly Hybrid Electrochemical Capacitors

Hybrid electrochemical capacitors have emerged as attractive energy storage option, which perfectly fill the gap between electric double-layer capacitors (EDLCs) and batteries, combining in one device the high power of the former and the high energy of the latter. We show that the charging characteristics of the positive carbon electrode are transformed to behave like a battery operating at nearly constant potential after it is polarized in aqueous iodide electrolyte (1 mol L−1 NaI). Thermogravimetric analysis of the positive carbon electrode confirms the decomposition of iodides trapped inside the carbon pores in a wide temperature range from 190 ◦C to 425 ◦C, while Raman spectra of the positive electrode show characteristic peaks of I3 − and I5 − at 110 and 160 cm−1 , respectively. After entrapment of polyiodides in the carbon pores by polarization in 1 mol L−1 NaI, the positive electrode retains the battery-like behavior in another cell, where it is coupled with a carbon-based negative electrode in aqueous NaNO3 electrolyte without any redox species. This new cell (the iodide-ion capacitor) demonstrates the charging characteristics of a hybrid capacitor with capacitance values comparable to the one using 1 mol L−1 NaI. The constant capacitance profile of the new hybrid cell in aqueous NaNO3 for 5000 galvanostatic charge/discharge cycles at 0.5 A g−1 shows that iodide species are confined to the positive battery-like electrode exhibiting negligible potential decay during self-discharge tests, and their shuttling to the negative electrode is prevented in this syste

Experimental investigation of segmented SOECs: Locally-resolved impedance and degradation characteristics

Abstract High temperature solid oxide electrolysis cells (SOEC) provide an innovative solution for direct conversion of steam and electricity to hydrogen with the addi- tional capability of adding CO2 to produce syngas. However, specific operating conditions can have a negative impact on the performance and lifetime of SOECs. In this context, the distributions of operational parameters such as gas species, temperature and current density within the cell structure influence local transport processes and reaction kinetics and can lead to locally different electrochemical potentials and thus degradation phenomena. This study focuses on experimental investigations of steam-electrode supported SOECs with segmented air electrodes with the main objective to measure EIS and thus identify locally-resolved impedance and degradation characteristics caused by different operating conditions in steam and co-electrolysis mode. Thereby, significant correlations between operating condi- tions, local effects, electrode processes and degradation mechanisms were observed and analyzed in detail using EIS,DRT and SEM.Keywords:Solid Oxide Electrolysis Cell (SOEC), Segmented, Locally-resolved, Electrochemical Analayis, Distribution of Relaxation Times (DR

Effects of high mechanical treatment and long-term annealing on crystal structure and thermal stability of Ti2O3nanocrystals

The effect of high-energy milling and long-term annealing on the stability of Ti2O3 nanocrystals was studied using a magnetic susceptibility method. In situ temperature dependences revealed that the crystal size greatly affects the magnetic susceptibility value. According to XRD, SEM and TEM data, Magnéli phases Ti9O10, Ti4O7, Ti7O19 and Ti3O5 are formed. © The Royal Society of Chemistry.Russian Foundation for Basic Research, RFBR: 19-03-00051aThe reported study was funded by RFBR according to the research project no. 19-03-00051a

Experimental identification of the impact of direct internal and external methane reforming on SOFC by detailed online monitoring and supporting measurements

Solid Oxide Fuel Cells (SOFCs) are able to use biogas or natural gas with its main compound methane as fuel but utilization of methane bears risks which can lead to early performance loss. Application of a suitable type of methane reforming as well as online monitoring tools and a holistic knowledge about possible degradation mechanisms can limit degradation rates. Here, we compare direct internal reforming and external methane reforming on a large planar SOFC with an active area of at different operating temperatures and methane flow rates. To do so, the measured temperature distribution, applied electrochemical impedance spectroscopy and its advanced tool distribution of relaxation times (DRT) as well as results from post mortem microscopic analysis are used. We observed that the ohmic resistance and high frequency peaks in the DRT spectra seem to be influenced not only by the average cell temperature but also by direct internal reforming (DIR) conditions. Furthermore, we observed that high temperature gradients induced by DIR could lead to or accelerate damages of the cells structure and the sealing. The results presented in this work are useful to control or manage safe SOFC operation with C containing fuels for real world SOFC applications