Overpotential

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

Electrospun Thin-Walled CuCo2O4@C Nanotubes as Bifunctional Oxygen Electrocatalysts for Rechargeable Zn–Air Batteries

Abstract: Rational design of optimal bifunctional oxygen electrocatalyst with low cost and high activity is greatly desired for realization of rechargeable Zn–air batteries. Herein, we fabricate mesoporous thin-walled CuCo2O4@C with abundant nitrogen-doped nanotubes via coaxial electrospinning technique. Benefiting from high catalytic activity of ultrasmall CuCo2O4 particles, double active specific surface area of mesoporous nanotubes, and strong coupling with N-doped carbon matrix, the obtained CuCo2O4@C exhibits outstanding oxygen electrocatalytic activity and stability, in terms of a positive onset potential (0.951 V) for oxygen reduction reaction (ORR) and a low overpotential (327 mV at 10 mA cm–2) for oxygen evolution reaction (OER). Significantly, when used as cathode catalyst for Zn-air batteries, CuCo2O4@C also displays a low charge–discharge voltage gap (0.79 V at 10 mA cm–2) and a long cycling life (up to 160 cycles for 80 h). With desirable architecture and excellent electrocatalytic properties, the CuCo...

Chemical and Electrochemical Differences in Nonaqueous Li–O2 and Na–O2 Batteries

Abstract: We present a comparative study of nonaqueous Li-O2 and Na-O2 batteries employing an ether-based electrolyte. The most intriguing difference between the two batteries is their respective galvanostatic charging overpotentials: a Na-O2 battery exhibits a low overpotential throughout most of its charge, whereas a Li-O2 battery has a low initial overpotential that continuously increases to very high voltages by the end of charge. However, we find that the inherent kinetic Li and Na-O2 overpotentials, as measured on a flat glassy carbon electrode in a bulk electrolysis cell, are similar. Measurement of each batteries' desired product yield, YNaO2 and YLi2O2, during discharge and rechargeability by differential electrochemical mass spectrometry (DEMS) indicates that less chemical and electrochemical decomposition occurs in a Na-O2 battery during the first Galvanostatic discharge-charge cycle. We therefore postulate that reactivity differences (Li2O2 being more reactive than NaO2) between the major discharge products lead to the observed charge overpotential difference between each battery.

Modulation of Inverse Spinel Fe 3 O 4 by Phosphorus Doping as an Industrially Promising Electrocatalyst for Hydrogen Evolution

Abstract: Fe-based oxides have been seldom reported as electrocatalysts for the hydrogen evolution reaction (HER), limited by their weak intrinsic activity and conductivity. Herein, phosphorus doping modulation is used to construct inverse spinel P-Fe3 O4 with dual active sites supported on iron foam (P-Fe3 O4 /IF) for alkaline HER with an extremely low overpotential of 138 mV at 100 mA cm-2 . The obtained inverse spinel Fe-O-P derived from controllable phosphorization can provide an octahedral Fe site and O atom, which bring about the unusual dissociation mechanisms of two water molecules to greatly accelerate the proton supply in alkaline media. Meanwhile, the ΔGH of the P atom in Fe-O-P as an active site is theoretically calculated to be 0.01 eV. Notably, the NiFe LDH/IF(+) ||P-Fe3 O4 /IF(-) couple achieves an onset potential of 1.47 V (vs RHE) for overall water splitting, with excellent stability for more than 1000 h at a current density of 1000 mA cm-2 , and even for 25 000 s at 10 000 mA cm-2 in 6.0 m KOH at 60 °C. The excellent catalyst stability and low-cost merits of P-Fe3 O4 /IF may hold promise for industrial hydrogen production. This work may reveal a new design strategy of earth-abundant materials for large-scale water splitting.

Overall photocatalytic water splitting with NiOx–SrTiO3 – a revised mechanism

Abstract: NiOx (0 < x < 1) modified SrTiO3 (STO) is one of the best studied photocatalysts for overall water splitting under UV light. The established mechanism for this and many other NiOx containing catalysts assumes water oxidation to occur at the early transition metal oxide and water reduction at NiOx. Here we show that NiOx–STO is more likely a three component Ni–STO–NiO catalyst, in which STO absorbs the light, Ni reduces protons, and NiO oxidizes water. This interpretation is based on systematic H2/O2 evolution tests of appropriately varied catalyst compositions using oxidized, chemically and photochemically added nickel and NiO nanoparticle cocatalysts. Surface photovoltage (SPV) measurements reveal that Ni(0) serves as an electron trap (site for water reduction) and that NiO serves as a hole trap (site for water oxidation). Electrochemical measurements show that the overpotential for water oxidation correlates with the NiO content, whereas the water reduction overpotential depends on the Ni content. Photodeposition experiments with NiCl2 and H2PtCl6 on NiO–STO show that electrons are available on the STO surface, not on the NiO particles. Based on photoelectrochemistry, both NiO and Ni particles suppress the Fermi level in STO, but the effect of this shift on catalytic activity is not clear. Overall, the results suggest a revised role of NiO in NiOx–STO and in many other nickel-containing water splitting systems, including NiOx–La : KTaO3, and many layered perovskites.