Polypyrrole Polyethylene Composite for Controllable Linear Actuators in Different Organic Electrolytes

Controllable linear actuation of polypyrrole (PPy) is the envisaged goal where only one ion dominates direction (here anions) in reversible redox cycles. PPy with polyethylene oxide (PEO) doped with dodecylbenzenesulfonate forms PPy-PEO/DBS films (PPy-PEO), which are applied in propylene carbonate (PC) solvent with electrolytes such as 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate (EDMICF3SO3), sodium perchlorate (NaClO4) and tetrabutylammonium hexafluorophosphate (TBAPF6) and compared in their linear actuation properties with pristine PPy/DBS samples. PPy-PEO showed for all applied electrolytes that only expansion at oxidation appeared in cyclic voltammetric studies, while pristine PPy/DBS had mixed-ion actuation in all electrolytes. The electrolyte TBAPF6-PC revealed for PPy-PEO best results with 18% strain (PPy/DBS had 8.5% strain), 2 times better strain rates, 1.8 times higher electronic conductivity, 1.4 times higher charge densities and 1.5 times higher diffusion coefficients in comparison to PPy/DBS. Long-term measurements up to 1000 cycles at 0.1 Hz revealed strain over 4% for PPy-PEO linear actuators, showing that combination of PPy/DBS with PEO gives excellent material for artificial muscle-like applications envisaged for smart textiles and soft robotics. FTIR and Raman spectroscopy confirmed PEO content in PPy. Electrochemical impedance spectroscopy (EIS) of PPy samples revealed 1.3 times higher ion conductivity of PPy-PEO films in PC solvent. Scanning electron microscopy (SEM) was used to investigate morphologies of PPy samples, and EDX spectroscopy was conducted to determine ion contents of oxidized/reduced films.

Redox Cycling for SOFC Accelerated Degradation

This work aims at development of Accelerated Stress Tests for SOFC via artificial aging of the fuel electrode applying chemical and electrochemical (hydrogen starvation) redox cycling. In principle the degradation processes follows that of calendar aging (Ni coarsening and migration), but in addition it can bring to irreversible damages caused by the development of cracks at the interface anode/electrolyte due to the expansion/shrinkage of the Ni network. The challenge is to introduce conditions which will prevent the formation of cracks which can be done by partial oxidation. The advantage of the proposed methodology is that a mild level of oxidation can be regulated by direct impedance monitoring of the Ni network resistance changes during oxidation/reduction. Once the redox cycling conditions are fixed on bare anode and checked on anode/electrolyte sample for eventual cracks, the procedure can be introduced for AST in full cell configuration. The developed methodology is evaluated by comparative impedance analysis of artificially aged and calendar aged button cells. The results for 20 redox cycles which can be performed for 24 hours are comparable with those obtained for about 1600 hours operation in standard conditions which ensures more than 50 times acceleration.

Kinetic Behavior of Fabricated CuO/ZrO2 Oxygen Carriers for Chemical Looping Oxygen Uncoupling

Chemical looping with oxygen uncoupling (CLOU) is an innovative alternative to conventional combustion. CuO/ZrO2 oxygen carriers were tested in this system for their effectiveness and resilience. Cupric oxide (CuO) was demonstrated to be a reliable oxygen carrier for oxygen-uncoupling with consistent recyclability even after 50 redox cycles in a thermogravimetric analyzer (TGA). The reduction of CuO to generate Cu2O and oxygen was observed to be improved markedly for experiments operated at higher temperatures; however, the oxidation of Cu2O by air to generate CuO was hindered for experiments carried out at elevated temperatures. The reduction rate of fabricated CuO/ZrO2 particles containing 40% CuO was enhanced with increasing temperature and decreased with increasing particle size for experiments operated in a fixed bed reactor. The geometrical contraction and Avrami-Erofe’ev models were demonstrated to be appropriate for describing the reduction and oxidation of CuO/ZrO2, respectively. The activation energies for the reduction and oxidation were determined to be 250.6 kJ/mol and 57.6 kJ/mol, respectively, based on experimental results in the temperature range between 850 and 1000 °C.

Bimetallic Cu/Fe Catalysts for Ibuprofen Mineralization

At present, the use of conventional wastewater processes is becoming increasingly challenging, mainly due to the presence of biorecalcitrant organic matter. Advanced oxidation processes such as Fenton, Fenton-like and hybrid processes have been successfully employed for the treatment of highly concentrated and toxic non-biodegradable pollutants. Here, a series of bimetallic catalysts, based on Cu/Fe supported over ZrO2, were investigated for the mineralization of ibuprofen with a heterogeneous Fenton-like reaction. The materials were prepared by incipient wetness impregnation and characterized by standard techniques. Temperature-programmed experiments highlighted the promotion of the reduction in CuO due to the synergistic effects of the coupled redox cycles of copper (Cu2+/Cu+) and iron (Fe+3/Fe+2). 5%Cu-5%Fe/ZrO2 not only displays the highest ibuprofen mineralization (83%) under optimum conditions but also exploits its activity in a wider range of pH (3–5) with extremely low metal leaching. The recycling of bimetallic catalysts reveals that only the 5%Cu-5%Fe/ZrO2 system is able to provide sustainable activity in heterogeneous Fenton process.

Effect of Mn and Cu Substitution on the SrFeO3 Perovskite for Potential Thermochemical Energy Storage Applications

Perovskites are well-known oxides for thermochemical energy storage applications (TCES) since they show a great potential for spontaneous O2 release due to their non-stoichiometry. Transition-metal-based perovskites are particularly promising candidates for TCES owing to their different oxidation states. It is important to test the thermal behavior of the perovskites for TCES applications; however, the amount of sample that can be used in thermal analyses is limited. The use of redox cycles in fluidized bed tests can offer a more realistic approach, since a larger amount of sample can be used to test the cyclic behavior of the perovskites. In this study, the oxygen release/consumption behavior of Mn- or Cu-substituted SrFeO3 (SrFe0.5M0.5O3; M: Mn or Cu) under redox cycling was investigated via thermal analysis and fluidized bed tests. The reaction enthalpies of the perovskites were also calculated via differential scanning calorimetry (DSC). Cu substitution in SrFeO3 increased the performance significantly for both cyclic stability and oxygen release/uptake capacity. Mn substitution also increased the cyclic stability; however, the presence of Mn as a substitute for Fe did not improve the oxygen release/uptake performance of the perovskite.

Self-regeneration of supported transition metals by a high entropy-driven principle

The sintering of Supported Transition Metal Catalysts (STMCs) is a core issue during high temperature catalysis. Perovskite oxides as host matrix for STMCs are proven to be sintering-resistance, leading to a family of self-regenerative materials. However, none other design principles for self-regenerative catalysts were put forward since 2002, which cannot satisfy diverse catalytic processes. Herein, inspired by the principle of high entropy-stabilized structure, a concept whether entropy driving force could promote the self-regeneration process is proposed. To verify it, a high entropy cubic Zr0.5(NiFeCuMnCo)0.5Ox is constructed as a host model, and interestingly in situ reversible exsolution-dissolution of supported metallic species are observed in multi redox cycles. Notably, in situ exsolved transition metals from high entropy Zr0.5(NiFeCuMnCo)0.5Ox support, whose entropic contribution (TΔSconfig = T⋆12.7 J mol−1 K−1) is predominant in ∆G, affording ultrahigh thermal stability in long-term CO2 hydrogenation (400 °C, >500 h). Current theory may inspire more STWCs with excellent sintering-resistance performance.

Relationship between microstructure and deformation of porous Ni-based cermets under redox cycling

This paper discusses the relationship between the elongation and compression behavior and microstructural changes under redox cycles of porous Ni(O)–YSZ cermets for solid oxide fuel cells (SOFC). Mechanical damage in SOFC and SOEC is one of the most important degradation factors governing the electrical performance of cells. Therefore, it is necessary to know the mechanical properties of each component material, such as elastic and deformation properties, in the operating environment. Particularly, of the Ni(O)–YSZ cermets which currently makes up 90% of the volume of the cell, with present mainstream anode supported SOFC and SOEC. Therefore, understanding the properties of the Ni(O)–YSZ cermets plays an important role in ensuring the performance of the entire SOFC and SOEC. In this study, the microstructural changes of Ni(O)–YSZ cermet by reduction, re-oxidation and re-reduction were observed in detail using microstructural observations and systematically compared with the dimensional change behavior. For the dimensional change behavior, a simple model considering the initial porosity and Ni content is proposed, which successfully predicts the dimensional change due to re-oxidation. Furthermore, Ni(O)–YSZ cermets with high Ni content show large initial dimensional changes, but the dimensional reversibility improves with increase of the number of redox cycles.