Overpotential

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

Nitrogen‐Doped Carbon Nanotube Arrays for High‐Efficiency Electrochemical Reduction of CO2: On the Understanding of Defects, Defect Density, and Selectivity

Abstract: Nitrogen-doped carbon nanotubes (NCNTs) have been considered as a promising electrocatalyst for carbon-dioxide-reduction reactions, but two fundamental chemistry questions remain obscure: 1) What are the active centers with respect to various defect species and 2) what is the role of defect density on the selectivity of NCNTs? The aim of this work is to address these questions. The catalytic activity of NCNTs depends on the structural nature of nitrogen in CNTs and defect density. Comparing with pristine CNTs, the presence of graphitic and pyridinic nitrogen significantly decreases the overpotential (ca. −0.18 V) and increases the selectivity (ca. 80 %) towards the formation of CO. The experimental results are in congruent with DFT calculations, which show that pyridinic defects retain a lone pair of electrons that are capable of binding CO2. However, for graphitic-like nitrogen, electrons are located in the π* antibonding orbital, making them less accessible for CO2 binding.

Se-Doping Activates FeOOH for Cost-Effective and Efficient Electrochemical Water Oxidation.

Abstract: Ni or Co is commonly required in efficient electrocatalysts for oxygen evolution reaction (OER). Although Fe is much more abundant and cheaper, full-Fe or Fe-rich catalysts suffer from insufficient activity. Herein, we discover that Se-doping can drastically promote OER on FeOOH and develop a facile on-site electrochemical activation strategy for achieving such a Se-doped FeOOH electrode via an FeSe precatalyst. Theoretical analysis and systematic experiments prove that Se-doping enables FeOOH as an efficient and low-cost OER electrocatalyst. By optimizing the electrode structure, an industrial-level OER current output of 500 mA cm-2 is secured at a low overpotential of 348 mV. The application of such an Fe-rich OER electrode in a practical solar-driven water splitting system demonstrates a high and stable solar-to-hydrogen efficiency of 18.55%, making the strategy promising for exploring new cost-effective and highly active electrocatalysts for clean hydrogen production.

Self-Supported FeP Nanorod Arrays: A Cost-Effective 3D Hydrogen Evolution Cathode with High Catalytic Activity

Abstract: Developing non-noble-metal hydrogen evolution reaction electrocatalysts with high activity is critical for future renewable energy systems. The direct growth of active phases on current collectors not only eliminates using polymer binder but also offers time-saving preparation of electrode. In this Letter, we develop self-supported FeP nanorod arrays on carbon cloth (FeP NAs/CC) via low-temperature phosphidation of its Fe2O3 NAs/CC. As a novel 3D hydrogen evolution cathode in acidic media, the FeP NAs/CC exhibits high catalytic activity and only needs an overpotential of 58 mV to afford current density of 10 mA/cm2. This electrode also works efficiently in both neutral and alkaline solutions.

Hierarchical ZnxCo3–xO4 Nanoarrays with High Activity for Electrocatalytic Oxygen Evolution

Abstract: The design and fabrication of efficient and inexpensive electrodes for use in the oxygen evolution reaction (OER) is essential for energy-conversion technologies. In this study, high OER performance is achieved using novel hierarchical ZnxCo3–xO4 nanostructures constructed with small secondary nanoneedles grown on primary rhombus-shaped pillar arrays. The nanostructures have large roughness factor, high porosity, and high active-site density. Only a small overpotential of ∼0.32 V is needed for a current density of 10 mA/cm2 with a Tafel slope of 51 mV/decade. The nanostructures are also found to perform significantly better than pure Co3O4 and a commercial Ir/C catalyst and to perform similarly to the best OER catalysts that have been reported for alkaline media. These merits combined with the satisfactory stability of the nanostructures indicate that they are promising electrodes for water oxidation.

Charge-Transfer Effects in Ni–Fe and Ni–Fe–Co Mixed-Metal Oxides for the Alkaline Oxygen Evolution Reaction

Abstract: Ni–Fe and Ni–Fe–Co mixed-metal oxide (MMO) films were investigated as electrocatalysts for the oxygen evolution reaction (OER) in 0.1 M KOH. In an effort to optimize MMO morphology, aniline was used as a capping agent to produce high-surface-area Ni–Fe–Co films on Raney nickel supports. This catalyst exhibits enhanced mass activity in comparison to the Ni–Fe OER electrocatalysts reported to date. Cyclic voltammetry shows changes in the potential of the Ni2+/3+ transitions in Fe- or Co-containing MMO films. In situ X-ray absorption spectroscopy (XAS) analysis confirms that Fe acts to stabilize Ni in the 2+ oxidation state, while Co facilitates oxidation to the 3+ state. The results of this study support the recent claims that Fe (not Ni) is the OER active site. The OER enhancement of the ternary Ni–Fe–Co catalyst results from two effects: (1) the charge-transfer effects of Co result in the formation of the conductive NiIIIOOH phase at lower overpotential, thus activating the Fe sites which are otherwise in...