Overpotential

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

Rational Catalyst and Electrolyte Design for Co2 Electroreduction Towards Multicarbon Products

Abstract: CO2 electroreduction reaction (CO2RR) to fuels and feedstocks is an attractive route to close the anthropogenic carbon cycle and store renewable energy. The generation of more reduced chemicals, especially multicarbon oxygenate and hydrocarbon products (C2+) with higher energy density is highly desirable for industrial applications. However, selective conversion of CO2 to C2+ suffers from high overpotential, low reaction rate and low selectivity, and the process is extremely sensitive to the catalyst structure and electrolyte. Here we discuss strategies to achieve high C2+ selectivity through rational design of the catalyst and electrolyte. Current state-of-the-art catalysts, including Cu and Cu-bimetallic catalysts as well as alternative materials are considered. The importance of taking into consideration the dynamic evolution of the catalyst structure and composition are highlighted, focusing on findings extracted from in situ and operando characterizations. Additional theoretical insight into the reaction mechanisms underlying the improved C2+ selectivity of specific catalyst geometries/compositions in synergy with a well-chosen electrolyte are also provided.

Cr-Doped FeNi-P Nanoparticles Encapsulated into N-Doped Carbon Nanotube as a Robust Bifunctional Catalyst for Efficient Overall Water Splitting.

Abstract: Exploring high-efficiency, stable, and cost-effective bifunctional electrocatalysts for overall water splitting is greatly desirable and challenging. Herein, a newly designed hybrid catalyst with Cr-doped FeNi-P nanoparticles encapsulated into N-doped carbon nanotubes (Cr-doped FeNi-P/NCN) with unprecedented electrocatalytic activity is developed by a simple one-step heating treatment. The as-synthesized Cr-doped FeNi-P/NCN with moderate Cr doping exhibits admirable oxygen evolution reaction and hydrogen evolution reaction activities with overpotentials of 240 and 190 mV to reach a current density of 10 mA cm-2 in 1 m KOH solution. When used in overall water splitting as a bifunctional catalyst, it needs only 1.50 V to give a current density of 10 mA cm-2 , which is superior to its typically integrated Pt/C and RuO2 counterparts (1.54 V @ 10 mA cm-2 ). Density functional theory calculation confirms that Cr doping into a FeNi-host can effectively alter the relative Gibbs adsorption energy and reduces the theoretical overpotential. Additionally, the synergetic effects between Cr-doped FeNi-P nanoparticles and NCNs are regarded as significant contributors to accelerate charge transfer and promote electrocatalytic activity in hybrid catalysts.

The Electrolytic Growth of Dendrites from Ionic Solutions

Abstract: Measurements have been made of the electrolytic growth on silver spheres of dendrites from the silver + silver nitrate system in liquid sodium nitrate + potassium nitrate. The potential and current density for initiation have been determined as a function of concentration and purity of the solution. Rates of growth have been measured as a function of potential at constant overpotential. The radius of the tips has been determined by electron microscopy. At constant current, the current density on to the base electrode during dendritic growth is proportional to the overpotential and the slope of the current density-overpotential relation is proportional to the concentration of silver ions. A critical current density ( i crit ) exists for initiation of dendritic growth. It is proportional to the silver ion concentration and increases as the radius of the substrate electrode decreases. i crit corresponds to an overpotential of 3 mV and increases with increasing purity of the solution. Dendrites are initiated up to 1 h after a constant current is switched on. At a given overpotential, a number of dendrites grow at a characteristic rate ( v ). Dendrites initiated at higher potential grow faster than those initiated at lower potential. The growing tip is parabolic and r tip ≏ 10 -5 cm. Twins are in some dendrites. The current density to the substrate is controlled by diffusion at all conditions and obeys laws characteristic of spherical diffusion for small radii of the substrate. The rate of growth of the dendrites is controlled by the kinetics of the Ag + ion deposition on the dendrite tip (activation and (spherical) diffusion control) and the effect on the Ag + + e ⇌ Ag reaction of the tip radius. For low exchange currents ( i 0 ) v ∝ η: for high i 0 , v α η 2 . The calculated rate of growth agrees with experimental data on maximum growth rate to some 50 %. The calculated r tip for maximum growth is essentially in agreement with that observed. At IηI r tip for maximum growth rate increases rapidly, and an alternative electrode process succeeds that of dendritic growth. The theory shows that the optimum radius for growth undergoes a rapid increase in the neighbourhood of the critical overpotential for cessation of growth. Dendrites are initiated only after a preliminary prismatic growth passes through the diffusion layer characteristic of the substrate electrode. Not all prismatic protrusions from the substrate are growth sites. Conditions for the stability of the tip shape during growth are deduced. Dendrites which grow with v less than v max are those with a stable r less than r opt . It is a good approximation to apply equations for diffusion to a stationary surface for the moving dendrite tip. The model is consistent with an observed increase in the number of dendrites with potential and with aspects of side-arm growth.

Highly stable Zn metal anodes enabled by atomic layer deposited Al 2 O 3 coating for aqueous zinc-ion batteries

Abstract: Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted increasing attention as an energy storage technology for large-scale applications, due to their high capacity (820 mA h g−1 and 5854 A h L−1), inherently high safety, and their low cost. However, the overall performance of ZIBs has been seriously hindered by the poor rechargeability of Zn anodes, because of the dendrite growth, passivation, and hydrogen evolution problems associated with Zn anodes. Herein, Al2O3 coating by an atomic layer deposition (ALD) technique was developed to address the aforementioned problems and improve the rechargeability of Zn anodes for ZIBs. By coating the Zn plate with an ultrathin Al2O3 layer, the wettability of Zn was improved and corrosion was inhibited. As a result, the formation of Zn dendrites was effectively suppressed, with a significantly improved lifetime in the Zn–Zn symmetric cells. With the optimized coating thickness of 100 cycles, 100Al2O3@Zn symmetric cells showed a reduced overpotential (36.5 mV) and a prolonged life span (over 500 h) at 1 mA cm−2. In addition, the 100Al2O3@Zn has been verified in Zn–MnO2 batteries using layered δ-MnO2 as the cathode and consequently exhibits superior electrochemical performance with a high capacity retention of 89.4% after over 1000 cycles at a current density of 1 mA cm−2 (3.33C for MnO2) was demonstrated. It is expected that the novel design of Al2O3 modified Zn anodes may pave the way towards high-performance aqueous ZIBs and shed light on the development of other metal anode-based battery systems.