NASICON (Na3Zr2Si2PO12)-based solid electrolyte-type sensors equipped with various metal oxides (MO)-added Pt sensing electrode (SE, Pt(nMO) (n: MO additive amount in wt%) and Pt counter electrode (CE, Pt) on the same side of the NASICON disc were fabricated and their (Pt(nMO)/Pt sensors) CO-sensing properties were examined at 25–300°C. The Pt(15Bi2O3)/Pt sensor showed the largest CO response with a change in electromotive force to a positive direction (positive response) at 25°C, while the Pt(15CeO2)/Pt sensor showed the largest negative CO response at 25°C. The CO response of the Pt(15CeO2)/Pt sensor seems to be determined by mixed potential at the triple phase boundaries (TPBs) containing the electrochemical reactions of CO oxidation and oxygen reduction. X-ray photoelectron spectroscopy of the Pt(15Bi2O3) SE before and after exposure to CO indicated a slight reduction of Bi3+ after the exposure to CO. Therefore, the additional electrochemical reactions containing the reduction of Bi2O3 were anticipated to occur at the TPBs of the Pt(15Bi2O3) SE, which resulted in the large positive CO response of the Pt(15Bi2O3)/Pt sensor. Furthermore, the addition of 15 wt% CeO2 to Pt CE of the Pt(15Bi2O3)/Pt sensor largely enhanced the magnitude of CO response and attained relatively excellent CO selectivity against H2.
From the viewpoint of the cost and safety, aqueous sodium-ion batteries are attractive candidate for large-scale energy storage. Although the operating voltage range of the aqueous battery is theoretically limited to 1.23 V by the electrochemical decomposition of water, the voltage restriction is a little bit eased in real aqueous battery system by the charge/discharge overvoltage. Effect of the concentrated electrolyte on the operation voltage was studied in aqueous Na-ion battery with Na2MnFe(CN)6 hexacyanoferrates cathode and NaTi2(PO4)3 NASICON-type anode, in order to increase the discharge voltage. According to the cyclic voltammetry, the electrochemical window of diluted 1 mol kg−1 NaClO4 aqueous electrolyte is only 1.9 V, whereas the corresponding electrochemical window of concentrated 17 mol kg−1 NaClO4 aqueous electrolyte is widen to 2.8 V. This wide electrochemical window of the concentrated aqueous electrolyte allows the Na2MnFe(CN)6//NaTi2(PO4)3 aqueous sodium-ion system to work reversibly. By contrast, the framework of Na2MnFe(CN)6 cathode was destroyed by the hydroxide anion generated in diluted 1 mol kg−1 electrolyte.
The fabrication process of porous copper (Cu) current collectors having the pore diameter (3–50 µm) and the rate of opening area (1–4%) was developed with a system constructed with a pico-second pulse laser and a polygon mirror. The fabricated porous Cu current collectors were used to evaluate the porous design on the Cu current collector for exhibiting higher Li+ doping reaction rate with cells in which graphite electrodes were laminated with separators and the laminated graphite anode opposites to Li metal through a separator. It was found in this study that the conditions of hole diameter (5 µm) and the rate of opening area (1%) is the best one to realize high Li+ doping rate and that the rate determining step of the pre-doping reaction is the diffusion of Li+ ion in the pore of the Cu porous current collectors.
The thermal stability of graphene has a close relationship with defect generation, thermal oxidation, which in turn have a significant bearing on its properties and applications. This report discusses the effect of confocal laser heating on the structure of single-layer graphene (SLG) on the basal plane and the edge. The thermal stability of SLG basal plane and edge was demonstrated to be different by using in situ anti-Stokes and Stokes Raman spectroscopy. The basal plane was found to be unstable above 500°C, while the edge could not endure even 220°C. The variation in the intensity of D, G, and 2D peaks and the intensity ratios of I(D)/I(G) and I(2D)/I(G) indicated that the thermal instability started with defect generation at the basal plane. The initial point defects at edge were partially eliminated at low temperature and generated again at temperatures above 220°C.