Stable blue suspensions of 2 nm diameter iridium oxide (IrO x 3 nH 2 O) nanoparticles were obtained by hydrolyzing IrCl 6 2-in base at 90°C to produce [Ir(OH) 6 ] 2-and then treating with HNO 3 at 0°C. UV-visible spectra show that acid condensation of [Ir(OH) 6 ] 2-results in quantitative conversion to stable, ligand-free IrO x 3 nH 2 O nanoparticles, which have an extinction coefficient of 630 ( 50 M -1 cm -1 at 580 nm. In contrast, alkaline hydrolysis alone converts only 30% of the sample to IrO x 3 nH 2 O at 2 mM concentration. The acidified nanoparticles are stable for at least one month at 2°C and can be used to make colloidal solutions between pH 1 and 13. At pH 7 and above, some hydrolysis to form [Ir(OH) 6 ] 2-occurs. Uniform IrO x 3 nH 2 O electrode films were grown anodically from pH 1 solutions, and were found to be highly active for water oxidation between pH 1 and 13.SECTION: Nanoparticles and Nanostructures R ecent research activity in artificial photosynthesis has intensified the search for water oxidation catalysts that can function at high turnover rates and low overpotentials. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Despite the high cost and low terrestrial abundance of iridium, hydrated iridium oxide (IrO x 3 nH 2 O) has been useful for fundamental studies of the water splitting reaction because it can be made as stable nanoparticles, and because it is highly active for water oxidation over a broad range of pH. [16][17][18][19][20][21][22][23][24][25][26] The synthesis of IrO x 3 nH 2 O colloids was first reported over 100 years ago, 27 and that synthetic method (alkaline hydrolysis of [IrCl 6 ] 2-) produces blue colloids with particle sizes in the 1-2 nm range. Recently, Murray and co-workers used this method to deposit electrode films of IrO x 3 nH 2 O, which they showed are very good electrocatalysts over a broad range of pH. 22,28 Alternative syntheses of IrO x 3 nH 2 O colloids have used stabilizing ligands with multiple carboxylate groups, such as malonate or succinate. 29-32 With these stabilizing ligands, the colloids may be incorporated into photoelectrodes and other assemblies for overall light-driven water splitting. 23,33-35 In syntheses using capping ligands, the yield of stable colloid is rarely quantitative, and some of the IrO x 3 nH 2 O precipitates as large particles. Similarly, in our hands the alkaline route to uncapped colloids gives solutions of varying color, from pale to deep blue. Another complication of current synthetic methods is that IrO x 3 nH 2 O nanoparticles are not stable under acidic conditions; for example citrate-capped IrO x 3 nH 2 O precipitates at pH < 3, 36 and ligandfree IrO x 3 nH 2 O nanoparticles synthesized by alkaline hydrolysis are unstable at neutral pH. 22 Because of these problems, we have conducted a study of the alkaline hydrolysis process, the results of which are reported here. We identify conditions for obtaining quantitative yields of catalytically active, uncapped colloids that are stable over a wide range of pH.Hydrolysis o...

All-solid-state batteries are often expected to replace conventional lithium-ion batteries in the future. However, the practical electrochemical and cycling stability of the best-conducting solid electrolytes, i.e. lithium thiophosphates, is still a critical issue that prevents long-term stable high-energy cells. In this study, we apply a stepwise cyclic voltammetry approach to obtain information on the practical oxidative stability limit of Li 10 GeP 2 S 12 , two different Li 2 S−P 2 S 5 glasses, as well as the argyrodite Li 6 PS 5 Cl solid electrolytes. We employ indium metal and carbon black as the counter and working electrodes, respectively, the latter to increase the interfacial contact area to the electrolyte as compared to the commonly used planar steel electrodes. Using a stepwise increase in the reversal potentials, the onset potential of oxidative decomposition at the electrode−electrolyte interface at 25 °C is identified. X-ray photoelectron spectroscopy is used to investigate the oxidation of sulfur(-II) in the thiophosphate polyanions to sulfur(0) as the dominant redox process in all electrolytes tested. Our results suggest that in later cycles the crystalline solid electrolyte itself is not the major redox active phase, but rather that only after the formation of such electrolyte decomposition products is significant redox behavior observed. Indeed, the redox behavior of the decomposition products is an additional contributor to the overall cell capacity of solid-state batteries. The stepwise cyclic voltammetry approach presented here shows that the practical oxidative stability at 25 °C of thiophosphate solid electrolytes against carbon is kinetically higher than predicted by thermodynamic calculations and that the decomposition products dominate the redox behavior of cathode composites. The method serves as an efficient guideline for the determination of practical, kinetic stability limits of solid electrolytes with respect to the employed electrode materials.

A facile, in-situ deposition route to stable iridium oxide (IrO(x)·nH(2)O) nanoparticle thin films from [Ir(OH)(6)](2-) solutions is reported. The [Ir(OH)(6)](2-) solution, made by alkaline hydrolysis of [IrCl(6)](2-), is colorless and stable near neutral pH, and forms blue IrO(x)·nH(2)O nanoparticle suspensions once it is adjusted to acidic or basic conditions. IrO(x)·nH(2)O nanoparticle thin films are grown anodically on glassy carbon, fluorine-doped tin oxide, and gold electrodes by electrolyzing [Ir(OH)(6)](2-) solutions at +1.0-1.3 V versus Ag/AgCl. The thickness of the IrO(x)·nH(2)O films can be controlled by varying the concentration of [Ir(OH)(6)](2-) , the deposition potential, and/or the deposition time. These thin films are stable between pH 1 and 13 and have the lowest overpotential (η) for the oxygen evolution reaction (OER) of any yet reported. Near neutral pH, the Tafel slope for the OER at a IrO(x)·nH(2)O film/Au rotating disk electrode was 37-39 mV per decade. The exchange current density for the OER was 4-8 × 10(-10) A cm(-2) at a 4 mC cm(-2) coverage of electroactive Ir.

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Solid and liquid electrolytes for electrochemical energy storage and conversion cells, such as batteries, supercapacitors and fuel cells, contain often high concentrations of mobile ions. Therefore, the ion dynamics in these electrolytes is characterized by pronounced directional correlations between successive ion movements, which exert a strong influence on charge and mass transport. In this manuscript, we review the relevant transport properties of (i) single-ion conducting solid electrolytes and of (ii) liquid electrolytes with a single type of cations and a single type of anions. All transport quantities are based on Onsager's linear irreversible thermodynamics and are defined in the laboratory frame of reference, so that they can be easily related to correlations functions of the equilibrium ion dynamics by means of linear response theory. In the case of single-cation conducting solid electrolytes, we discuss how the complex interplay between cation-cation and cation-lattice interactions leads to a competition between cation self-correlations and distinct-cation correlations. In the case of liquid electrolytes, we describe how cation-cation, anion-anion, and cation-anions correlations influence the various transport quantities, such as total ionic conductivity, Haven ratio, salt diffusion coefficient and cation transference numbers. Moreover, we discuss how, in dilute liquid electrolytes, ion correlations can be governed by ion pair formation. Finally, the competition between cation/ anion and cation/polymer chain interactions can lead to negative cation transference numbers in polymer electrolytes, i. e. to cations migrating towards the positive electrode. Taken together, these case studies showcase how ion correlations in electrolyte systems can strongly influence the overall efficiency of energy storage and conversion devices due to transport limitations.[a] Dr.