Search

A Bi2O3 is a promising material for a supercapacitor negative electrode. A typical surfactant for synthesizing Bi2O3 via a hydrothermal method is ethylene glycol (EG); however, polyethylene glycol (PEG) has not been employed. In this study, three different glycol-based surfactants including EG, PEG400, and PEG600 were compared based on their effects on the phase, morphology, and supercapacitive properties of hydrothermal Bi2O3 (160 °C, 3 h). Along with δ-Bi2O3, Bi2O2CO3 also formed. The as-synthesized δ-Bi2O3/Bi2O2CO3 (BiEG, BiPEG400, and BiPEG600) had different morphological features but these structures were altered after grinding. Increasing the molecular weight of the surfactant reduced the carbonate phase, providing better connectivity between the electrode material and the current collector as well as lowering a charge transfer resistance. As a result, the BiPEG600 electrode exhibited the best electrochemical properties in terms of capacitance and retention. This also highlighted the importance of charge transfer and morphology, which overshadowed the Brunauer–Emmett–Teller (BET) surface area. Specifically, the BiPEG600 capacitance was 969 F g−1 at 1 A g−1, and was retained at 46% after 2000 cycles at 50 A g−1. Promising specific capacitances obtained at high discharge rates of 50 and 60 A g−1 were 436 and 381 F g−1, respectively. [ABSTRACT FROM AUTHOR]

Copper samarium co-doped ceria (CSDC) (Cu0.01Sm0.19Ce0.80O2−δ) nanoparticles were synthesized via a sol-gel auto-combustion of metal nitrates without a complexing agent (DI) and with tartaric acid (TA) or citric acid (CA). The solid oxide formation of CSDC/DI corresponds to the endothermic stage, whereas that of CSDC/TA and CSDC/CA matches the exothermic stage caused by the decomposition of the metal cross-linking and carbon combustion. The cross-linking occurs more extensively in the CA case as more heat is released in CA than in the TA route. The as-synthesized morphology of CSDC/DI reveals both layered structures and small agglomerated particles, whereas CSDC/TA and CSDC/CA show dense xerogel and porous xerogel, respectively. The cubic fluorite structure for calcined CSDCs was confirmed by XRD. From Raman analysis, calcined CSDC/CA has the lowest amount of copper segregation and the highest relative total oxygen vacancy concentration [ V O • • ]total, whereas calcined CSDC/DI has the highest amount of copper segregation and the lowest [ V O • • ]total. For all samples, copper segregation promotes densification, albeit to varying degrees. The relative densities of CSDC/DI, CSDC/TA, and CSDC/CA pellets are 82.8 ± 2.4%, 95.5 ± 1.8%, and 97.8 ± 0.9%, respectively. The sintered CSDC/DI has the lowest density because some copper segregates and liquid copper in interparticle spaces could evaporate earlier than samples containing a complexing agent, whereas sintered CSDC/CA has the highest density because Cu could slowly diffuse from the Cu-Sm-Ce solid solution to grain boundary regions and then precipitate as CuO. The specific grain boundary conductivity is predominantly influenced by CuO along grain boundaries, which reduces specific grain boundary conductivity and increases the enthalpy of association (ΔHa) at 250–350°C; however, it rarely impacts total grain boundary conductivity at temperatures higher than 400°C. CSDC/CA has slightly higher total conductivity than CSDC/TA despite having more CuO segregation because it has higher density and V O • • . [ABSTRACT FROM AUTHOR]