Overpotential

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

Metal Oxide Photoelectrodes for Solar Fuel Production, Surface Traps, and Catalysis

Abstract: The photoelectrochemical reduction of water or CO2 is a promising route to sustainable solar fuels but hinges on the identification of a stable photoanode for water oxidation. Semiconductor oxides like Fe2O3 and BiVO4 have been gaining significant attention as promising materials. However, they exhibit a major drawback of a large required overpotential for solar water oxidation. In this Perspective, recent efforts to characterize and reduce the overpotential are critically examined. The accumulation of photogenerated holes at the semiconductor–liquid interface, recently observed with multiple techniques, is rationalized with surface state models. Transient absorption spectroscopy and electrochemical impedance spectroscopy suggest that surface treatments designed to either passivate surface traps or increase reaction rates (as catalysts) actually perform identically. This calls into question the definition of a catalyst when coupled to a semiconductor photoelectrode. In contrast, results from transient pho...

Dual-Functional N Dopants in Edges and Basal Plane of MoS2 Nanosheets Toward Efficient and Durable Hydrogen Evolution

Abstract: Herein, the authors explicitly reveal the dual-functions of N dopants in molybdenum disulfide (MoS2) catalyst through a combined experimental and first-principles approach. The authors achieve an economical, ecofriendly, and most efficient MoS2-based hydrogen evolution reaction (HER) catalyst of N-doped MoS2 nanosheets, exhibiting an onset overpotential of 35 mV, an overpotential of 121 mV at 100 mA cm-2 and a Tafel slope of 41 mV dec(-1). The dual-functions of N dopants are (1) activating the HER catalytic activity of MoS2 S-edge and (2) enhancing the conductivity of MoS2 basal plane to promote rapid charge transfer. Comprehensive electrochemical measurements prove that both the amount of active HER sites and the conductivity of N-doped MoS2 increase as a result of doping N. Systematic first-principles calculations identify the active HER sites in N-doped MoS2 edges and also illustrate the conducting charges spreading over N-doped basal plane induced by strong Mo 3d-S 2p-N 2p hybridizations at Fermi level. The experimental and theoretical research on the efficient HER catalysis of N-doped MoS2 nanosheets possesses great potential for future sustainable hydrogen production via water electrolysis and will stimulate further development on nonmetal-doped MoS2 systems to bring about novel high-performance HER catalysts.

Efficient and Robust Carbon Dioxide Electroreduction Enabled by Atomically Dispersed Sn δ + Sites.

Abstract: Electrocatalytic CO2 reduction at considerably low overpotentials still remains a great challenge. Here, a positively charged single-atom metal electrocatalyst to largely reduce the overpotentials is designed and hence CO2 electroreduction performance is accelerated. Taking the metal Sn as an example, kilogram-scale single-atom Snδ + on N-doped graphene is first fabricated by a quick freeze-vacuum drying-calcination method. Synchrotron-radiation X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy demonstrate the atomically dispersed Sn atoms are positively charged, which enables CO2 activation and protonation to proceed spontaneously through stabilizing CO2 •- * and HCOO- *, affirmed by in situ Fourier transform infrared spectra and Gibbs free energy calculations. Furthermore, N-doping facilitates the rate-limiting formate desorption step, verified by the decreased desorption energy from 2.16 to 1.01 eV and the elongated SnHCOO- bond length. As an result, single-atom Snδ + on N-doped graphene exhibits a very low onset overpotential down to 60 mV for formate production and shows a very large turnover frequency up to 11930 h-1 , while its electroreduction activity proceeds without deactivation even after 200 h. This work offers a new pathway for manipulating electrocatalytic performance.

Reversibility and efficiency in electrocatalytic energy conversion and lessons from enzymes

Abstract: Enzymes are long established as extremely efficient catalysts. Here, we show that enzymes can also be extremely efficient electrocatalysts (catalysts of redox reactions at electrodes). Despite being large and electronically insulating through most of their volume, some enzymes, when attached to an electrode, catalyze electrochemical reactions that are otherwise extremely sluggish (even with the best synthetic catalysts) and require a large overpotential to achieve a useful rate. These enzymes produce high electrocatalytic currents, displayed in single bidirectional voltammetric waves that switch direction (between oxidation and reduction) sharply at the equilibrium potential for the substrate redox couple. Notoriously irreversible processes such as CO2 reduction are thereby rendered electrochemically reversible—a consequence of molecular evolution responding to stringent biological drivers for thermodynamic efficiency. Enzymes thus set high standards for the catalysts of future energy technologies.