Overpotential

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

Hierarchically porous Co3O4/C nanowire arrays derived from a metal–organic framework for high performance supercapacitors and the oxygen evolution reaction

Abstract: Transition metal oxides with hierarchically porous structures supported by conductive substrates have been considered as promising electrodes for electrochemical energy storage and catalysis. Herein we configure porous Co3O4/C nanowire arrays (NAs) by thermally annealing a Co-based metal–organic framework (Co-MOF) in Ar and air, respectively. The hybrid Co3O4/C NAs demonstrate a high specific capacitance of 1.32 F cm−2 at a current density of 1 mA cm−2, which is much superior to that of bare Co3O4 NAs. A highly stable symmetric supercapacitor based on Co3O4/C exhibits an excellent durability with only 21.7% capacitance decay after 5000 cycles. Besides electrochemical energy storage, the Co3O4/C hybrids demonstrate an outstanding electrochemical catalysis ability for the oxygen evolution reaction, identified by the high current density of 30 mA cm−2 at low overpotential (η30 = 318 mV) and a small Tafel slope (81 mV dec−1). The electrical conductivity of the interconnected C infrastructures and ion diffusion within the hierarchical pores are intrinsic causes to promote the pseudo-capacitive performance and enhance catalytic activity. The synthesis strategy reported here opens an avenue to design high performance electrodes for energy storage and electrochemical catalysis.

Hydrogen evolution from neutral water under aerobic conditions catalyzed by cobalt microperoxidase-11.

Abstract: A molecular electrocatalyst is reported that reduces protons to hydrogen (H2) in neutral water under aerobic conditions. The biomolecular catalyst is made from cobalt substitution of microperoxidase-11, a water-soluble heme-undecapeptide derived from the protein horse cytochrome c. In aqueous solution at pH 7.0, the catalyst operates with near quantitative Faradaic efficiency, a turnover frequency ∼6.7 s–1 measured over 10 min at an overpotential of 852 mV, and a turnover number of 2.5 × 104. Catalyst activity has low sensitivity to oxygen. The results show promise as a hydrogenase functional mimic derived from a biomolecule.

Cobalt Iron Hydroxide as a Precious Metal-Free Bifunctional Electrocatalyst for Efficient Overall Water Splitting

Abstract: Highly efficient and stable electrocatalysts from inexpensive and earth-abundant elements are emerging materials in the overall water splitting process. Herein, cobalt iron hydroxide nanosheets are directly deposited on nickel foam by a simple and rapid electrodeposition method. The cobalt iron hydroxide (CoFe/NF) nanosheets not only allow good exposure of the highly active surface area but also facilitate the mass and charge transport capability. As an anode, the CoFe/NF electrocatalyst displays excellent oxygen evolution reaction catalytic activity with an overpotential of 220 mV at a current density of 10 mA cm-2 . As a cathode, it exhibits good performance in the hydrogen evolution reaction with an overpotential of 110 mV, reaching a current density of 10 mA cm-2 . When CoFe/NF electrodes are used as the anode and the cathode for water splitting, a low cell voltage of 1.64 V at 10 mA cm-2 and excellent stability for 50 h are observed. The present work demonstrates a possible pathway to develop a highly active and durable substitute for noble metal electrocatalysts for overall water splitting.

Diode-like behaviour of a mitochondrial electron-transport enzyme.

Abstract: In mitochondria, electrons derived from the oxidation of succinate by the tricarboxylic acid cycle enzyme succinate-ubiquinone oxido-reductase are transferred directly to the quinone pool. Here we provide evidence that the soluble form of this enzyme (succinate dehydrogenase) behaves as a diode that essentially allows electron flow in one direction only. The gating effect is observed when electrons are exchanged rapidly and directly between fully active succinate dehydrogenase and a graphite electrode. Turnover is therefore measured under conditions of continuously variable electrochemical potential. The otherwise rapid and efficient reduction of fumarate (the reverse reaction) is severely retarded as the driving force (overpotential) is increased. Such behaviour can arise if a rate-limiting chemical step like substrate binding or product release depends on the oxidation state of a redox group on the enzyme. The observation provides, for a biological electron-transport system, a simple demonstration of directionality that is enforced by kinetics as opposed to that which is assumed from thermodynamics.

In situ encapsulation of core–shell-structured Co@Co3O4 into nitrogen-doped carbon polyhedra as a bifunctional catalyst for rechargeable Zn–air batteries

Abstract: The traditional oxygen reduction/evolution reaction (ORR/OER) catalysts are mainly noble metal-based materials, but their scarcity and instability impede their practical applications, especially in Zn–air batteries. Hence, identifying a bifunctional catalyst with low-cost and high-stability is very crucial for Zn–air batteries. Herein, we report a simple method to prepare core–shell-structured Co@Co3O4 nanoparticles encapsulated into N-doped carbon polyhedra by carbonization and controlled oxidation of metal–organic frameworks (MOFs), which are then applied as a bifunctional catalyst for Zn–air batteries. Using such a configuration, enhanced performances, including a high power density of ∼64 mW cm−2, a stable voltage profile over 80 h battery operation with four mechanical recharges, a small discharge/charge overpotential of ∼0.66 V and a long-life of 100 cycles for 200 h operation at 5 mA cm−2, have been achieved. These excellent performances can be attributed to abundant graphited carbon and CNTs, high N-doping, plentiful pores, the synergy between the semiconductive Co3O4-coating layer and the conductive Co bulk, and the uniform Co@Co3O4 nanoparticles in this catalyst which effectively improve electrical conductivity/ion transfer and further concertedly promote the catalytic activity towards the ORR/OER. Moreover, the belt-shaped polymer Zn–air battery with this catalyst also shows good electrochemical stability under different deformations.