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Aqueous electrolytes are attractive for applications in electrochemical technologies due to features like being eco‐friendly, cost effective, and non‐flammable. Very recently, superconcentrated aqueous electrolytes, such as so‐called water‐in‐salt, water‐in‐bisalt, and hydrate melt, have received a significant attention for electrochemical energy storage due to enhanced stability and much wider electrochemical stability window. This Review focuses on the physicochemical properties of the highly concentrated electrolytes that are derived from several analysis techniques and simulation. A summary of most common features such as ions‐water interactions, structure of species present in the electrolyte, conductivity, and viscosity of the electrolytes found in the literature are presented as well. In addition, this Review explains how these characteristics affect the electrochemical behavior of the electrolyte such as double layer structure and electrode/electrolyte interface leading to enhanced electrochemical stability of aqueous electrolytes.

One of the major challenges associated with fuel cells is the design of highly efficient electrocatalysts to reduce the high overpotential of the oxygen reduction reaction (ORR). In this study, a facile photoassisted method was employed for the direct deposition of palladium nanoparticles (Pd NPs) onto graphitic carbon nitride (g-C 3 N 4 ) for efficient oxygen reduction. The fabricated catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Fourier transmission infrared (FTIR) spectroscopy. The electrocatalytic activity of the prepared catalysts was examined using cyclic voltammetry (CV), linear scan voltammetry (LSV), and chronoamperometry (CA). Our studies have shown that the synthesized Pd-g-C 3 N 4 nanocomposite exhibited robust electrocatalytic behavior toward the ORR in 0.1 M KOH solution, where the desirable fourelectron pathway was achieved. This enhanced ORR activity might be attributed to synergetic effects between g-C 3 N 4 and Pd as well as the even dispersion of the small Pd NPs. In addition, the developed catalyst demonstrated a significantly improved tolerance against methanol as well as enhanced stability in comparison to the benchmark commercial platinum-loaded carbon catalysts. INTRODUCTIONGiven the critical degradative environmental impacts of traditional energy sources, there is a great interest to develop clean, cost-effective, and efficient energy technologies. One potential solution toward addressing global energy demands comprises fuel cell technologies. The potential applications of fuel cells are extensive as they have the capacity to provide clean energy and sustainable power. 1 Fuel cells directly utilizes fuels (e.g., hydrogen, methanol, formic acid) and oxygen and effectively convert their chemical energy into electricity with a high power density. 2 The difficult challenges associated with fuel cells relate to the development of highly active electrocatalysts to reduce the high overpotential at the cathode during the ORR. 3 Platinum (Pt) is considered as one of the preeminent electrocatalysts for ORR. Unfortunately, the limited availability and expense of Pt are major constraints that limit its wide commercial applications. 4 There have been significant advancements made in the elucidation of ORR on Pt-based nanomaterials; however, they still struggle with severe stability and consistency issues, together with crossover and poisoning effects in the cathodic compartments of the direct methanol fuel cell, which result in a decrease in the performance of the catalysts. 5 Therefore, it is necessary to identify alternate new materials and methodologies to overcome costs related issues and to enhance the catalytic performance of electrocatalysts. 6,7 Graphitic carbon nitride (g-C 3 N 4 ) has a planar structure similar to graphite. 8 It includes both pyridinic and graphitic nitrogen moieties, w...

1,10-phenanthroline is grafted to indium tin oxide (ITO) and titanium dioxide nanoparticle (TiO) semiconductors by electroreduction of 5-diazo-1,10-phenanthroline in 0.1 M HSO. The lower and upper potential limits (-0.20 and 0.15 V, respectively) were set to avoid reduction and oxidation of the 1,10-phenanthroline (phen) covalently grafted at C5 to the semiconductor. The resulting semiconductor-phen ligand (ITO-phen or TiO-phen) was air stable, and was bonded to Ru- or Ir- by reaction with cis-[Ru(bpy)(CHCN)] (bpy = 2,2'-bipyridine) or cis-[Ir(ppy)(CHCN)] (ppy = ortho-C metalated 2-phenylpyridine) in CHCl and THF solvent at 50 °C. Cyclic voltammetry, X-ray photoelectron spectroscopy, solid-state UV-vis, and inductively coupled plasma-mass spectrometry all confirmed that the chromophores SC-[(phen)Ru(bpy)] and SC-[(phen)Ir(ppy)] (SC = ITO or TiO) formed in near quantitative yields by these reactions. The resulting photoanodes were active and relatively stable to photoelectrochemical oxidation of hydroquinone and triethylamine under neutral and basic conditions.

The organic carbazole−cyanobenzene push−pull dye 1,2,3,5tetrakis(carbazol-9-yl)-4,6-dicyanobenzene was derivatized and attached to carbon or indium-doped tin oxide (ITO) electrodes by simple diazonium electrografting. The surface-bound dye is active and stable for the visible light photosynthetic isomerization of a wide range of functionalized stilbene and cinnamic acid derivatives. Up to 87,000 net turnovers were obtained for the isomerization of trans-stilbene. The isomerizations can be carried out in air with a 33% reduction in the rate. The ITO photoelectrodes are also active and stable toward photo-oxidations under basic and acidic conditions.