The largest increases in capacitance occurred for samples with a moderate initial copper content combined with a small amount of copper removal, resulting in numerous small pits in the post-dealloy topography. The

largest capacitance ratio observed for these samples implies a factor of 3 increase in surface area after dealloying. Hydrogen evolution reaction measurements To characterize the catalytic behavior of the samples, HER measurements were made both before and after dealloying. Example Tafel plots of the data are shown in buy BVD-523 Figure 6. In general for these samples, the HER current density is larger after dealloying for low overpotentials, but smaller after dealloying for larger overpotentials. That is, the dealloyed samples are more reactive at lower overpotentials but less reactive at higher overpotentials for HER measurements. In addition, the Staurosporine data show a range of Tafel slopes for the

overpotential range measured. This effect is more significant for the as-deposited samples. Figure 6 HER measurements of two samples both before and after the dealloying process. Current densities were calculated SIS3 cell line with respect to the geometric area of the sample. The initial copper content in the films are (a) 12.6±0.6% and (b) 21.4±1.1%. The copper content in the dealloyed films are (a) 11.4±0.6% and (b) 13.9±0.7%. For each set of measurements, the high overpotential data (between -350 and -200 mV) were fit to the Tafel equation, J = J 0 e −B η , where J is the current density and η is the overpotential. The Tafel slope, , and exchange current density, J 0, were determined from the fit parameters. The results are shown in Figure 7 as a function of the Cu composition initially in the sample. Consistent with the data in Figure 6, the samples tend to have both higher Tafel slope and higher exchange current density after dealloying compared to their as-deposited counterparts. This combination causes the crossing of the HER curves in Figure 6, where the dealloyed samples are more reactive at lower overpotentials and less reactive

at higher overpotentials. Figure 7 Tafel slope and current density cAMP extracted from HER measurements. (a) Tafel slope and (b) exchange current density from HER measurements of the as-deposited and dealloyed NiCu thin films as a function of Cu content in the film before dealloying. For the as-deposited samples, the Tafel slopes tend to be around 100 to 125 mV/dec. In contrast, the Tafel slopes for the dealloyed samples are generally higher, most above 175 mV/dec. One possible reason for these larger Tafel slopes is a decrease in effective area available for reaction at higher overpotentials due to larger gas evolution rates. This effect may be increased by the more porous nature of the dealloyed samples, allowing gas bubbles to be trapped more easily.