An Electrochemical Actuator Fabricated by Transfer-printing of a Carbon Electrode onto a Cupric-ion-containing Poly(acrylic acid) Gel Surface

Highly functional polymer-gel materials that include highly conductive gels, moving gels, and stimulation-responsive gels are important in a number of applications, including actuators, microrobots, and artificial muscle; hence, the development of new gels with superior properties is an important objective. Herein, we report the fabrication of a flexible electrochemical actuator by the direct transfer of a carbon electrode, formed by screen-printing on a silicone sheet, onto the surface of a poly(acrylic acid) gel containing cupric ions, which was prepared by immersing the poly(acrylic acid) gel in a 0.1 mM copper sulfate solution. Due to the oxidation of copper and the reduction of cupric ions, when potentials of 0.6 V and −0.7 V are alternately applied to the poly(acrylic acid)-cupric-ion gel actuator, it repeatedly expands and contracts along with concomitant copper-ion redox transformations when immersed in 0.1 M aqueous sodium perchlorate. This actuator demonstrated a 0.29% change in expansion ratio, which is 2.3-times larger than that of a previously reported electrochemical actuator (0.13%) formed with a sputtered gold electrode on a conventional polymer substrate

Iridium(III) Bis-Pyridine-2-Sulfonamide Complexes as Efficient and Durable Catalysts for Homogeneous Water Oxidation

A family of tetradentate bis­(pyridine-2-sulfonamide) (bpsa) compounds was synthesized as a ligand platform for designing resilient and electronically tunable catalysts capable of performing water oxidation catalysis and other processes in highly oxidizing environments. These wrap-around ligands were coordinated to Ir­(III) octahedrally, forming an anionic complex with chloride ions bound to the two remaining coordination sites. NMR spectroscopy documented that the more rigid ligand frameworks[Ir­(bpsa-Cy)­Cl₂]⁻ and [Ir­(bpsa-Ph)­Cl₂]⁻produced <i>C</i>₁-symmetric complexes, while the complex with the more flexible ethylene linker in [Ir­(bpsa-en)­Cl₂]⁻ displays <i>C</i>₂ symmetry. Their electronic structure was explored with DFT calculations and cyclic voltammetry in nonaqueous environments, which unveiled highly reversible Ir­(III)/Ir­(IV) redox processes and more complex, irreversible reduction chemistry. Addition of water to the electrolyte revealed the ability of these complexes to catalyze the water oxidation reaction efficiently. Electrochemical quartz crystal microbalance studies confirmed that a molecular species is responsible for the observed electrocatalytic behavior and ruled out the formation of active IrO_<i>x</i>. The electrochemical studies were complemented by work on chemically driven water oxidation, where the catalytic activity of the iridium complexes was studied upon exposure to ceric ammonium nitrate, a strong, one-electron oxidant. Variation of the catalyst concentrations helped to illuminate the kinetics of these water oxidation processes and highlighted the robustness of these systems. Stable performance for over 10 days with thousands of catalyst turnovers was observed with the <i>C</i>₁-symmetric catalysts. Dynamic light scattering experiments ascertained that a molecular species is responsible for the catalytic activity and excluded the formation of IrO_<i>x</i> particles