Mixed Fe−Ni oxide electrocatalysts for the oxygen evolution reaction in alkaline electrolytes were synthesized using three different approaches: evaporation induced self-assembly, hard templating, and dip-coating. For each synthesis method, a peak in oxygen evolution activity was observed near 10 mol % Fe content, where the mixed metal oxide was substantially more active than the parent metal oxide electrocatalysts. X-ray diffraction (XRD) analysis showed the formation of a mixed NiO/NiFe 2 O 4 phase at low Fe concentrations, and formation of Fe 2 O 3 at compositions above 25 mol % Fe. Raman vibrational spectroscopy confirmed the formation of NiFe 2 O 4 , and did not detect Fe 2 O 3 in the electrocatalysts containing up to 20 mol % Fe. X-ray absorption near edge structure (XANES) showed the Fe in the mixed oxides to be predominantly in the +3 oxidation state. Extended X-ray absorption fine structure (EXAFS) showed changes in the Fe coordination shells under electrochemical oxygen evolution conditions. Temperature programmed reaction spectroscopy showed the mixed oxide surfaces also have superior oxidation activity for methanol oxidation, and that the reactivity of the mixed oxide surface is substantially different than that of the parent metal oxide surfaces. Overall, the NiFe 2 O 4 phase is implicated in having a significant role in improving the oxygen evolution activity of the mixed metal oxide systems.

To enhance performance stability, carbon electrodes with opposite net surface charges were employed to develop the inverted capacitive deionization system.

Commercially available activated carbon cloth electrodes are treated using nitric acid and ethylenediamine solutions, resulting in chemical surface charge enhanced carbon electrodes for capacitive deionization (CDI) applications. Surface charge enhanced electrodes are then configured in a CDI cell to examine their salt removal at a fixed charging voltage and both reduced and opposite polarity discharge voltages, and subsequently compared to the salt removal of untreated electrodes. Substantially improved salt removal due to chemical surface charge and the use of a discharge voltage of opposite sign to the charging voltage is clearly demonstrated in these CDI cycling tests, an observation which for the first time validates both enhanced CDI and extended-voltage CDI effects predicted by the Donnan model [Biesheuvel et al., Colloids Interf. Sci. Comm., 10.1016/j.colcom.2015.12.001 (2016)]. Our experimental and theoretical results demonstrate that the use of carbon electrodes with optimized chemical surface charge can extend the CDI working voltage window through discharge voltages of opposite sign to the charging voltage, which can significantly enhance the salt adsorption capacity of CDI electrodes. Thus, in addition to carbon pore size distribution, chemical surface charge in carbon micropores is considered foundational for salt removal in CDI cells.

Electrochemical impedance spectroscopy and cyclic voltammetry were used to investigate the electrode kinetics of V II -V III and V IV -V V in H 2 SO 4 on glassy carbon, carbon paper, carbon xerogel, and carbon fibers. It was shown that, for all carbon materials investigated, the kinetics of V II -V III is enhanced by anodic, and inhibited by cathodic, treatment of the electrode; in contrast, the kinetics of V IV -V V is inhibited by anodic, and enhanced by cathodic, treatment. The potential region for each of these effects varied only slightly with carbon material. Rate constants were always greater for V IV -V V than for V II -V III except when anodized electrodes were compared, which may explain discrepancies in the literature. The observed effects are attributed to oxygen-containing functional-groups on the electrode surface. The considerable differences between the potentials at which enhancement of V II -V III and inhibition of V IV -V V occur indicates that they do not correspond to a common oxidized state of the electrode. Likewise inhibition of V II -V III and enhancement of V IV -V V do not correspond to a common reduced state of the electrode. It is possible that enhancement of both V II -V III and V IV -V V is due to the same (active) state of the electrode. There is considerable interest in vanadium flow batteries (VFBs), also known as vanadium redox flow batteries (VRFBs or VRBs), for storage of electrical energy particularly in conjunction with renewable energy sources such as wind and solar. [1][2][3][4][5][6] Active areas of research include cell design and modelling, [7][8][9] performance and state-of-charge monitoring, 10-16 coulombic and energy efficiencies, 5,17,18 electrolytes, [11][12][13][14][15][16]19,20 membranes, 4,21 and electrodes. Cells typically have porous carbon electrodes and electrode performance can depend strongly on electrode treatment. Various electrochemical, 22-27,36-41 chemical, 36,40,43,44 and thermal [45][46][47][48][49] treatments have been reported. These treatments often have the effect of oxidizing or reducing the surface, and the influence of surface oxygen species on electrochemical kinetics at carbon electrodes is recognized, 22,57-60 although often not well understood. Thermal 45-49 and chemical 36,40,43,44 treatments of electrodes for VFBs have been tested on a range of carbon-based electrodes and, in general, these treatments result in higher activities of the electrode toward the vanadium redox reactions. There are also a number of reports of the effect of electrochemical treatment of electrodes. Anodic treatment of carbon felt was reported 22,36 to cause a decrease in the kinetic rates of the V IV -V V redox couple. In contrast, there are also reports of enhancement of V IV -V V kinetics after electrochemical oxidation [38][39][40][41] (of graphite and carbon felt electrodes) and of V II -V III kinetics after potential cycling 61 (of highly-oriented-pyrolytic-graphite and glassy carbon electrodes). However, in considering the effects of anodization on a c...