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: Polyethylenimine functions as a co-catalyst by significantly reducing catalytic overpotential and increasing current density and efficiency and appears to help in stabilizing the singly reduced intermediate CO2(•-) and concentrating CO2 in the PEI overlayer.
Abstract: Nitrogen-doped carbon nanotubes are selective and robust electrocatalysts for CO2 reduction to formate in aqueous media without the use of a metal catalyst. Polyethylenimine (PEI) functions as a co-catalyst by significantly reducing catalytic overpotential and increasing current density and efficiency. The co-catalysis appears to help in stabilizing the singly reduced intermediate CO2(•-) and concentrating CO2 in the PEI overlayer.
555 citations
TL;DR: In this article, the authors demonstrate that robust bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity can be achieved by inducing lattice strain in noble-metal-free metal-organic frameworks (MOFs).
Abstract: Oxygen electrocatalysis is central to technologies such as fuel cells and electrolysers, but challenges remain due to the lack of effective earth-abundant electrocatalysts and insufficient understanding of catalytic mechanisms. Here we demonstrate that robust bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity can be achieved by inducing lattice strain in noble-metal-free metal–organic frameworks (MOFs). Lattice-strained NiFe MOFs exhibit mass activities of 500 A gmetal−1 at a half-wave potential of 0.83 V for the ORR and 2,000 A gmetal−1 at an overpotential of 0.30 V for the OER, which are 50–100 times that of pristine NiFe metal–organic frameworks. The catalyst maintains ~97% of its initial activity after 200 h of continuous ORR/OER reaction at a high current density of 100–200 mA cm−2. Using operando synchrotron spectroscopies, we observed a key superoxide *OOH intermediate emerging on Ni4+ sites during both the ORR and OER processes, which suggests a four-electron mechanistic pathway. Metal–organic frameworks (MOFs) are increasingly being explored as electrocatalysts for the oxygen evolution and reduction reactions, which are important processes in electrolysers and fuel cells. Here, the authors increase the activity of MOFs for these reactions by introducing strain into the lattice using UV light illumination.
555 citations
TL;DR: In this article, a concept whereby graphene defects trap atomic Ni species inside to form an integrity (aNi@defect) was reported, and the derived catalyst exhibits exceptionally good activity for both HER and OER, e.g., an overpotential of 70 mV at 10 mA/cm2 for HER (analogous to the commercial Pt/C) and 270 mV for OER (much superior to that of Ir oxide).
555 citations
TL;DR: A novel type of robust cobalt-nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template is reported.
Abstract: Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. Here we report a novel type of robust cobalt–nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template. We identify the well-dispersed molecular CoNx sites on the carbon support as the active sites responsible for the HER. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s−1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Our results suggest the great promise of developing new families of non-precious metal HER catalysts based on the controlled conversion of homogeneous metal complexes into solid-state carbon catalysts via economically scalable protocols. Hydrogen evolution from water promises a future clean energy source, however the cost of noble metal catalysts, which are necessary for high efficiency, are very expensive. Here, the authors fabricate a porous cobalt–nitrogen/carbon catalyst which can deliver high activity and stability but at reduced cost.
552 citations
TL;DR: In this article, the point defect model was extended to account for chemical breakdown, and the dependence of the breakdown potential on halide concentration and incubation time breakdown overpotential relationships was investigated.
Abstract: The point defect model that was previously developed (1) to explain the growth kinetics of a passive film has been extended to account for chemical breakdown. This model provides quantitative explanations of the dependence of breakdown potential on halide concentration, and of the incubation time‐breakdown overpotential relationships that have been observed for iron and nickel in aqueous solutions. Limitations of the model are identified and discussed.
551 citations