Overpotential

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

Electrochemical Reduction of CO2 Catalyzed by Fe-N-C Materials: A Structure–Selectivity Study

Abstract: Selective electrochemical reduction of CO2 into energy-dense organic compounds is a promising strategy for using CO2 as a carbon source. Herein, we investigate a series of iron-based catalysts synthesized by pyrolysis of Fe-, N-, and C-containing precursors for the electroreduction of CO2 to CO under aqueous conditions and demonstrate that the selectivity of these materials for CO2 reduction over proton reduction is governed by the ratio of isolated FeN4 sites vs Fe-based nanoparticles. This ratio can be synthetically tuned to generate electrocatalysts producing controlled CO/H2 ratios. It notably allows preparing materials containing only FeN4 sites, which are able to selectively reduce CO2 to CO in aqueous solution with Faradaic yields of over 90% and at low overpotential.

Ultrathin High Surface Area Nickel Boride (NixB) Nanosheets as Highly Efficient Electrocatalyst for Oxygen Evolution

Abstract: The overriding obstacle to mass production of hydrogen from water as the premium fuel for powering our planet is the frustratingly slow kinetics of the oxygen evolution reaction (OER). Additionally, inadequate understanding of the key barriers of the OER is a hindrance to insightful design of advanced OER catalysts. This study presents ultrathin amorphous high-surface area nickel boride (NixB) nanosheets as a low-cost, very efficient and stable catalyst for the OER for electrochemical water splitting. The catalyst affords 10 mA cm−2 at 0.38 V overpotential during OER in 1.0 m KOH, reducing to only 0.28 V at 20 mA cm−2 when supported on nickel foam, which ranks it among the best reported nonprecious catalysts for oxygen evolution. Operando X-ray absorption fine-structure spectroscopy measurements reveal prevalence of NiOOH, as well as Ni-B under OER conditions, owing to a Ni-B core@nickel oxyhydroxide shell (Ni-B@NiOxH) structure, and increase in disorder of the NiOxH layer, thus revealing important insight into the transient states of the catalyst during oxygen evolution.

NiCoFe Layered Triple Hydroxides with Porous Structures as High-Performance Electrocatalysts for Overall Water Splitting

Abstract: We report a type of NiCoFe layered triple hydroxides (LTHs) supported on carbon fiber cloth (CFC) (NiCoFe LTHs/CFC) as high-performance electrocatalysts for overall water splitting in alkaline media. The NiCoFe LTHs/CFC as an oxygen evolution reaction (OER) electrocatalyst shows excellent catalytic activity and durability, such as low overpotential of ∼239 mV at 10 mA cm–2, small Tafel slope of ∼32 mV dec–1 and conservation rate of catalytic activity (∼99%) after 12 h of continuous electrolysis at 20 mA cm–2. As a hydrogen evolution reaction (HER) electrocatalyst, NiCoFe LTHs/CFC also shows low onset potential, small Tafel slope, and superior durability. The NiCoFe LTHs/CFC-based overall water splitting exhibits a low onset potential (∼1.51 V), a low splitting potential (∼1.55 V) at 10 mA cm–2, and excellent durability, and the performance is comparable to that of IrO2/Pt-based overall water splitting. This work will open a new avenue toward the development of high-performance and inexpensive layered trip...

Thick Electrodes for High Energy Lithium Ion Batteries

Abstract: Lithium ion cells have undergone a remarkable development regarding energy density, power density, lifetime, safety and costs since their market introduction in the early 1990s. While the early applications focused mainly on consumer electronics, in the second half of the last decade electromobile and stationary energy storage applications moved into scope. Today the industry focuses strongly on cost targets in terms of dollars per Watthour, by lowering both material and production costs and increasing the energy density of the cells while maintaining other factors such as safety and lifetime constant on a high level. Three different cell designs are usually considered for electromobile or stationary energy applications: (i) cylindrical cells, (ii) prismatic shaped cells in hard cases made from metal or plastics, and (iii) pouch bag or coffee bag cells. The latter are widely used and are typically 7 to 13 mm thick which correlates with a few dozen layers of anode and cathode sheets, depending whether they are designed to serve energy or power optimized purposes. To produce such a stack, electrodes need to be cut from an electrode roll for example via laser cutting or punching, cleaned from loose particles, picked up automatically and then placed alternately with high accuracy on top of the growing stack. Compared to other steps in cell production like tab welding, pouch foil packaging and sealing or electrolyte filling, this stapling process takes up a considerable amount of the total cell assembly time. With the goal of reducing the stack assembly time and increasing the throughput of the cutting and stacking machine we have considered to investigate the preparation and characterization of electrodes that are substantially thicker than conventional ones and which would decrease the number of sheets for an electrode stack of given capacity. However, with increasing electrode thickness the mass transport limitations of lithium ions in the electrolyte phase as well as the impedance for electrons in the solid phase of the electrode become dominating. This will reduce the capacity of the cell due to higher overpotentials upon charging and discharging within fixed voltage limits. At the same time, the geometric current density in the separator is higher at a given C-rate for thick electrodes compared to thin ones which causes additional overpotential and, in case of charging, could lead tolithiumplating ongraphite particles invicinitytotheseparator. The concept of thick electrodes has been employed previously 1, 2, 3