Overpotential

About: Overpotential is a research topic. Over the lifetime, 16474 publications have been published within this topic receiving 616632 citations.

An Efficient and Earth-Abundant Oxygen-Evolving Electrocatalyst Based on Amorphous Metal Borides

Abstract: Cost-effective and efficient oxygen-evolving electrocatalysts are urgently required for energy storage and conversion technologies. In this work, an amorphous trimetallic boride nanocatalyst (Fe–Co–2.3Ni–B) prepared by a simple approach is reported as a highly efficient oxygen evolution reaction electrocatalyst. It exhibits an overpotential (η) of 274 mV to deliver a geometric current density (jgeo) of 10 mA cm−2, a small Tafel slope of 38 mV dec−1, and excellent long-term durability at a mass loading of 0.3 mg cm−2. The impressive electrocatalytic performance originates from the unique amorphous multimetal–metalloid complex nanostructure. From application's point of view, this work holds great promise as this process is simple and allows for large-scale production of cheap, yet efficient, material.

Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes

Abstract: The compound CsH2PO4 has emerged as a viable electrolyte for intermediate temperature (200–300 °C) fuel cells. In order to settle the question of the high temperature behavior of this material, conductivity measurements were performed by two-point AC impedance spectroscopy under humidified conditions (p[H2O] = 0.4 atm). A transition to a stable, high conductivity phase was observed at 230 °C, with the conductivity rising to a value of 2.2 × 10−2 S cm−1 at 240 °C and the activation energy of proton transport dropping to 0.42 eV. In the absence of active humidification, dehydration of CsH2PO4 does indeed occur, but, in contradiction to some suggestions in the literature, the dehydration process is not responsible for the high conductivity at this temperature. Electrochemical characterization by galvanostatic current interrupt (GCI) methods and three-point AC impedance spectroscopy (under uniform, humidified gases) of CsH2PO4 based fuel cells, in which a composite mixture of the electrolyte, Pt supported on carbon, Pt black and carbon black served as the electrodes, showed that the overpotential for hydrogen electrooxidation was virtually immeasurable. The overpotential for oxygen electroreduction, however, was found to be on the order of 100 mV at 100 mA cm−2. Thus, for fuel cells in which the supported electrolyte membrane was only 25 μm in thickness and in which a peak power density of 415 mW cm−2 was achieved, the majority of the overpotential was found to be due to the slow rate of oxygen electrocatalysis. While the much faster kinetics at the anode over those at the cathode are not surprising, the result indicates that enhancing power output beyond the present levels will require improving cathode properties rather than further lowering the electrolyte thickness. In addition to the characterization of the transport and electrochemical properties of CsH2PO4, a discussion of the entropy of the superprotonic transition and the implications for proton transport is presented.

Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials

Abstract: In a comparative study of the electrocatalytic CO2 reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.

Iridium Single Atoms Coupling with Oxygen Vacancies Boosts Oxygen Evolution Reaction in Acid Media

Abstract: Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of electrocatalysis oxygen evolution reaction (OER) in acid. Herein, we report a novel strategy to prepare iridium single-atoms (Ir-SAs) on ultrathin NiCo2O4 porous nanosheets (Ir-NiCo2O4 NSs) by the co-electrodeposition method. The surface-exposed Ir-SAs couplings with oxygen vacancies (VO) exhibit boosting the catalysts OER activity and stability in acid media. They display superior OER performance with an ultralow overpotential of 240 mV at j = 10 mA cm-2 and long-term stability of 70 h in acid media. The TOFs of 1.13 and 6.70 s-1 at an overpotential of 300 and 370 mV also confirm their remarkable performance. Density functional theory (DFT) calculations reveal that the prominent OER performance arises from the surface electronic exchange-and-transfer activities contributed by atomic Ir incorporation on the intrinsic VO existed NiCo2O4 surface. The atomic Ir sites substantially elevate the electronic activity of surface lower coordinated Co sites nearby VO, which facilitate the surface electronic exchange-and-transfer capabilities. With this trend, the preferred H2O activation and stabilized *O have been reached toward competitively lower overpotential. This is a generalized key for optimally boosting OER performance.

MOF-derived Co-doped nickel selenide/C electrocatalysts supported on Ni foam for overall water splitting

Abstract: It is of prime importance to develop dual-functional electrocatalysts with good activity for overall water splitting, which remains a great challenge. Herein, we report the synthesis of a Co-doped nickel selenide (a mixture of NiSe2 and Ni3Se4)/C hybrid nanostructure supported on Ni foam using a metal–organic framework as the precursor. The resulting catalyst exhibits excellent catalytic activity toward the oxygen evolution reaction (OER), which only requires an overpotential of 275 mV to drive a current density of 30 mA cm−2. This overpotential is much lower than those reported for precious metal free OER catalysts. The hybrid is also capable of catalyzing the hydrogen evolution reaction (HER) efficiently. A current density of −10 mA cm−2 can be achieved at 90 mV. In addition, such a hybrid nanostructure can achieve 10 and 30 mA cm−2 at potentials of 1.6 and 1.71 V, respectively, along with good durability when functioning as both the cathode and the anode for overall water splitting in basic media.