Overpotential

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

Coordination engineering of iridium nanocluster bifunctional electrocatalyst for highly efficient and pH-universal overall water splitting

Abstract: Water electrolysis offers a promising energy conversion and storage technology for mitigating the global energy and environmental crisis, but there still lack highly efficient and pH-universal electrocatalysts to boost the sluggish kinetics for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we report uniformly dispersed iridium nanoclusters embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for both HER and OER at all pH conditions, reaching a current density of 10 mA cm−2 with only 300, 190 and 220 mV overpotential for overall water splitting in neutral, acidic and alkaline electrolyte, respectively. Based on probing experiments, operando X-ray absorption spectroscopy and theoretical calculations, we attribute the high catalytic activities to the optimum bindings to hydrogen (for HER) and oxygenated intermediate species (for OER) derived from the tunable and favorable electronic state of the iridium sites coordinated with both nitrogen and sulfur. Water electrolysis offers a promising energy conversion technology, although there is still a need to understand the catalysis on the atomic-level. Here, the authors report Ir nanoclusters coordinated with both N and S as an efficient and pH-universal electrocatalyst for overall water splitting.

Nitrogen doped NiFe layered double hydroxide/reduced graphene oxide mesoporous nanosphere as an effective bifunctional electrocatalyst for oxygen reduction and evolution reactions

Abstract: It is a crucial and challengeable task to develop non-precious metal catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in energy storage and conversion systems. Herein, a facile and cost-effective strategy was employed to prepare the mesoporous nitrogen doped NiFe layered double hydroxide/reduced graphene oxide (NiFe-LDH/NrGO) nanospheres via an one-pot solvothermal reaction by using GO, protonated g-C3N4 nanosheets (p-CNNS), mixed metal salts and alkali as precursors in presence of surfactant. The doping of p-CNNS resulted in the superior ORR activity compared to pristine NiFe-LDH and NiFe-LDH/rGO. The ORR results demonstrated that the NiFe-LDH/NrGO hybrid involved a perfect 4e mechanism with better durability and methanol tolerance ability than commercial 20% Pt/C catalyst in 0.1 M KOH. NiFe-LDH/NrGO also displayed the excellent OER activity with a close onset overpotential to NiFe-LDH/rGO, but a more negative overpotential and a higher current density at η > 300 mV in the same alkaline medium. Overall, the outstanding catalytic performance toward both ORR and OER suggested that the NiFe-LDH/NrGO composite can be a new non-precious metal bifunctional catalyst in the related renewable energy fields.

Morphology of Template-Grown Polyaniline Nanowires and Its Effect on the Electrochemical Capacitance of Nanowire Arrays

Abstract: The morphology of polyaniline nanowires grown electrochemically in anodic aluminum oxide (AAO) templates is strongly influenced by the supporting electrolyte concentration, the potential of electropolymerization, the growth time, and the monomer concentration. Increasing the sulfuric acid concentration during growth induces a transition from solid nanowires with tubular ends to open nanowires. Current transient data for nanowire growth were interpreted quantitatively in terms of instantaneous and progressive nucleation and growth models, and this analysis was consistent with the observed concentration and potential dependence of nanowire vs nanotube growth. The electrochemical capacitance of nanowire arrays in AAO templates was shown to be related to the morphology of the nanowires. Specific capacitance values in the range of 700 F/g (measured at a charge/discharge rate of 5 A/g) were obtained for porous nanowires grown at 0.5 M aniline concentration at high overpotential in 1.5−2.0 M sulfuric acid solutions.

Dominating Role of Ni0 on the Interface of Ni/NiO for Enhanced Hydrogen Evolution Reaction

Abstract: The research of a robust catalytic system based on single NiOx electrocatalyst for hydrogen evolution reaction (HER) remains a huge challenge. Particularly, the factors that dominate the catalytic properties of NiOx-based hybrids for HER have not been clearly demonstrated. Herein, a convenient protocol for the fabrication of NiOx@bamboo-like carbon nanotube hybrids (NiOx@BCNTs) is designed. The hybrids exhibit superb catalytic ability and considerable durability in alkaline solution. A benchmark HER current density of 10 mA cm–2 has been achieved at an overpotential of ∼79 mV. In combination with the experimental results and density functional theory (DFT) calculations, this for the first time definitely validates that the inherent high Ni0 ratio and the Ni0 on the interface of Ni/NiO play a vital role in the outstanding catalytic performance. Especially, the Ni0 on the interface of Ni/NiO performs superior activity for water splitting compared with that of bulk Ni0. These conclusions provide guidance for...