Topic
Overpotential
About: Overpotential is a research topic. Over the lifetime, 16474 publications have been published within this topic receiving 616632 citations.
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TL;DR: In this article, a two-step reaction for preparing hydrogen evolution reaction (HER) electrodes composed of Pt nanoparticles and MoS2 nanosheets grown on carbon fibers is described.
227 citations
TL;DR: In this article, the authors used sum frequency generation (SFG) to explore the mechanism of the enhancement of selectivity of a 1-ethyl-3methylimidazolium tetrafluoroborate (EMIM-BF4)-coated silver catalyst.
Abstract: Lowering the overpotential for the electrochemical conversion of CO2 to useful products is one of the grand challenges in the Department Of Energy report, “Catalysis for Energy”. In a previous paper, we showed that CO2 conversion occurs at low overpotential on a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4)-coated silver catalyst in an aqueous solution of EMIM-BF4. One of the surprises in the previous paper was that the selectivity to CO was better than 96% on silver, compared with ∼80% in the absence of ionic liquid. In this article, we use sum frequency generation (SFG) to explore the mechanism of the enhancement of selectivity. The study used platinum rather than silver because previous workers had found that platinum is almost inactive for CO production from CO2. The results show that EMIM-BF4 has two effects: it suppresses hydrogen formation and enhances CO2 conversion. SFG shows that there is a layer of EMIM on the platinum surface that inhibits hydrogen formation. CO2, however, can react...
226 citations
TL;DR: This work fabricates a core-shell heterostructure with an ultrathin shell (4 nm) and favorable exposure of active sites, resulting in a moderately regulated electronic structure, remarkably facilitated charge transfer, fully exposedactive sites, and a strongly coupled heterointerface for energy electrocatalysis.
Abstract: A cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalyst will be significant for the future energy scenario. The emergence of the core-shell heterostructure has invoked new feasibilities to inspire the full potential of non-precious-metal candidates. The shells always have a large thickness, affording robust mechanical properties under harsh reaction conditions, which limits the full exposure of active sites with highly intrinsic reactivity and extrinsic physicochemical characters for optimal performance. Herein, a nanosized CoNi hydroxide@hydroxysulfide core-shell heterostructure is fabricated via an ethanol-modified surface sulfurization method. Such a synthetic strategy is demonstrated to be effective in controllably fabricating a core-shell heterostructure with an ultrathin shell (4 nm) and favorable exposure of active sites, resulting in a moderately regulated electronic structure, remarkably facilitated charge transfer, fully exposed active sites, and a strongly coupled heterointerface for energy electrocatalysis. Consequently, the as-obtained hydroxide@hydroxysulfide core-shell is revealed as a superior OER catalyst, with a small overpotential of 274.0 mV required for 10.0 mA cm-2 , a low Tafel slope of 45.0 mV dec-1 , and a favorable long-term stability in 0.10 M KOH. This work affords fresh concepts and strategies for the design and fabrication of advanced core-shell heterostructures, and thus opens up new avenues for the targeted development of high-performance energy materials.
226 citations
TL;DR: This model suggests that different facets, terminations, and sites may dominate in charge relative to those for discharge, and there are other predicted paths for discharge/charge that have higher overpotentials, so the phase space available for the electrochemistry opens up with overpotential.
Abstract: We develop a density functional theory model for the electrochemical growth and dissolution of Li2O2 on various facets, terminations, and sites (terrace, steps, and kinks) of a Li2O2 surface. We argue that this is a reasonable model to describe discharge and charge of Li-O2 batteries over most of the discharge-charge cycle. Because non-stoichiometric surfaces are potential dependent and since the potential varies during discharge and charge, we study the thermodynamic stability of facets, terminations, and steps as a function of potential. This suggests that different facets, terminations, and sites may dominate in charge relative to those for discharge. We find very low thermodynamic overpotentials (<0.2 V) for both discharge and charge at many sites on the facets studied. These low thermodynamic overpotentials for both discharge and charge are in very good agreement with the low kinetic overpotentials observed in recent experiments. However, there are other predicted paths for discharge/charge that have higher overpotentials, so the phase space available for the electrochemistry opens up with overpotential.
226 citations
TL;DR: Although the initial aim was to improve electrocatalytic activity by greatly boosting the active area of the Ni-S catalyst, the performance enhancements instead were found to arise primarily from the ability of the proton-conductive MOF to favourably modify the immediate chemical environment of the sulfide-based catalyst.
Abstract: The availability of efficient hydrogen evolution reaction (HER) catalysts is of high importance for solar fuel technologies aimed at reducing future carbon emissions. Even though Pt electrodes are excellent HER electrocatalysts, commercialization of large-scale hydrogen production technology requires finding an equally efficient, low-cost, earth-abundant alternative. Here, high porosity, metal-organic framework (MOF) films have been used as scaffolds for the deposition of a Ni-S electrocatalyst. Compared with an MOF-free Ni-S, the resulting hybrid materials exhibit significantly enhanced performance for HER from aqueous acid, decreasing the kinetic overpotential by more than 200 mV at a benchmark current density of 10 mA cm(-2). Although the initial aim was to improve electrocatalytic activity by greatly boosting the active area of the Ni-S catalyst, the performance enhancements instead were found to arise primarily from the ability of the proton-conductive MOF to favourably modify the immediate chemical environment of the sulfide-based catalyst.
226 citations