Mesoporous Carbons for Energy-Efficient Water Splitting to Produce Pure Hydrogen at Room Temperature

Theoretical and experimental aspects of the use of mesoporous carbons in carbon-assisted water electrolysis (CAWE) to produce pure hydrogen at room temperature are presented. It is shown that the electrical energy requirements for CAWE can be as low as 20% of the energy needed for conventional water electrolysis, the extra energy coming from the electrochemical oxidation of carbon occurring at room temperature. Although CO2 is produced at the anode in this process, it is well separated from pure H2 produced at the cathode. Experimental results are reviewed for a variety of carbons with the major focus on the results obtained with carbon BP2000, which has both mesopores and micropores and a nanocarbon produced by the hydrothermal treatment of microcrystalline cellulose

Optimized Analysis of the AC Magnetic Susceptibility Data in Several Spin-Glass Systems using the Vogel-Fulcher and Power Laws

In spin-glasses (SG), the relaxation time $\tau$ ($= 1/2{\pi}f$) vs. $T_f$ data at the peak position $T_f$ in the temperature variation of the ac magnetic susceptibilities at different frequencies f is often fit to the Vogel-Fulcher Law (VFL): $\tau=\tau_0\exp[E_a/k_b(T_f-T_0)]$ and to the Power Law (PL): $\tau = \tau_0^*[(T_f-T_{SG}/T_{SG}]^{-z\nu}$. Both these laws have three fitting parameters each, leaving a degree of uncertainty since the magnitudes of the evaluated parameters $\tau_0$, $E_a/k_B$, $\tau_{0^*}$ and $z\nu$ depend strongly on the choice of $T_0$ and $T_{SG}$. Here we report an optimized procedure for the analysis of $\tau$ vs. $T_f$ data on several SG systems for which we could extract such data from published sources. In this optimized method, the data of $\tau$ vs. $T_f$ are fit by varying $T_0$ in the linear plots of $\ln \tau$ vs $1/ (T_f - T_0)$ for the VFL and by varying $T_{SG}$ in the linear plot of $\ln \tau$ vs. $\ln (T_f - T_{SG})/ T_{SG}$ for the PL till optimum fits are obtained. The analysis of the associated magnitudes of $\tau_0$, $E_a/k_B$, $\tau_{0^*}$ and $z\nu$ for these optimum values of $T_0$ and $T_{SG}$ shows that magnitudes of $\tau_{0^*}$, $\tau_0$ and $z\nu$ fail to provide a clear distinction between canonical and cluster SG. However, new results emerge showing $E_a/(k_BT_0) < 1$ in canonical SG whereas $E_a/(k_BT_0) >1$ for cluster SG systems and the optimized $T_0 <$ optimized $T_{SG}$ in all cases. Although some interpretation of these new results is presented, a more rigorous theoretical justification of the boundary near $E_a/(k_BT_0) \sim 1$ is desired along with testing of these criteria in other SG systems.Comment: 33 pages, 4 main figures, 15 figures in the supplementary document. The following article has been submitted to AIP Advance

Magnetic properties of Fe-doped CuAlO2 and role of impurities

The delafossite CuAlO2 is a rare p-type semiconductor with potential applications as a thermoelectric and as a dilute magnetic semiconductor when doped with transition metal ions. Reported here are results from our investigations of CuAl1-xFexO2 (x = 0, 0.01, 0.05, and 0.1) with a focus on the x-dependence of structural and magnetic properties, and role of impurities. The samples prepared by the solid-state reaction at 1,100°C were characterized by X-ray diffraction (XRD), energy dispersive (X-ray) spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The magnetic results show that the Curie constant (C), low temperature magnetization (M) and the lattice constants scale with x. High resolution M-H loop measurements at 300 K and 10 K show negligible coercivity HCat 10 K but HC ∼ 100 Oe at 300K. These results suggest the presence of minute quantities of hematite (α-Fe2O3) that are not detected in our XRD and XPS. The role of impurities on the published results in this system is discussed