Overpotential

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

Pd-Containing Nanostructures for Electrochemical CO2 Reduction Reaction

Abstract: The electrochemical CO2 reduction reaction (CO2RR), with water as a hydrogen source, has been attracting great attention due to its promising applications for carbon recycle utilization and renewable electricity storage. In order to drive the process economically, highly efficient catalysts are urgently needed to overcome the constraints of high overpotential, low Faradaic efficiency, and current density of CO2RR. This Perspective summarizes the performance of Pd-containing nanostructures toward CO2RR and related reaction mechanisms. The product selectivity of the Pd catalysts strongly depends on the structure and composition, and the dynamic evolution of active phases induced by the applied potential and reaction intermediate of CO2RR. Introducing a second metal can effectively suppress the decay in the catalytic performance of a Pd catalyst and further improve the activity and selectivity of CO2RR. The electrochemical promotion of catalysis effect drastically improves the production rate of formate over...

High Surface Area Stainless Steel Brushes as Cathodes in Microbial Electrolysis Cells

Abstract: Microbial electrolysis cells (MECs) are an efficient technology for generating hydrogen gas from organic matter, but alternatives to precious metals are needed for cathode catalysts. We show here that high surface area stainless steel brush cathodes produce hydrogen at rates and efficiencies similar to those achieved with platinum-catalyzed carbon cloth cathodes in single-chamber MECs. Using a stainless steel brush cathode with a specific surface area of 810 m2/m3, hydrogen was produced at a rate of 1.7 +/- 0.1 m3-H2/m3-d (current density of 188 +/- 10 A/m3) at an applied voltage of 0.6 V. The energy efficiency relative to the electrical energy input was 221 +/- 8%, and the overall energy efficiency was 78 +/- 5% based on both electrical energy and substrate utilization. These values compare well to previous results obtained using platinum on flat carbon cathodes in a similar system. Reducing the cathode surface area by 75% decreased performance from 91 +/- 3 A/m3 to 78 +/- 4 A/m3. A brush cathode with graphite instead of stainless steel and a specific surface area of 4600 m2/m3 generated substantially less current (1.7 +/- 0.0 A/m3), and a flat stainless steel cathode (25 m2/m3) produced 64 +/- 1 A/m3, demonstrating that both the stainless steel and the large surface area contributed to high current densities. Linear sweep voltammetry showed that the stainless steel brush cathodes both reduced the overpotential needed for hydrogen evolution and exhibited a decrease in overpotential over time as a result of activation. These results demonstrate for the first time that hydrogen production can be achieved at rates comparable to those with precious metal catalysts in MECs without the need for expensive cathodes.

Two-step synthesis of binary Ni–Fe sulfides supported on nickel foam as highly efficient electrocatalysts for the oxygen evolution reaction

Abstract: A facile two-step method has been used to synthesize binary Ni–Fe sulfides supported on nickel foam (NF) as electrocatalysts for the oxygen evolution reaction (OER). Firstly, NiFe hydroxide nanosheets have been electrodeposited on NF (NiFe/NF) as a precursor with a large surface area. Secondly, the as-prepared NiFe/NF has been subjected to a hydrothermal sulfuration process in order to prepare NiFeS/NF as an efficient electrocatalyst for the OER. The as-prepared samples have been characterized by XRD, XPS and SEM. The SEM images show that the NiFeS film was composed of needle-like nanostructures covering the surface of the NF. The corresponding OER performances in alkaline media have been systematically investigated. NiFeS/NF shows a superior overpotential of 65 mV at 10 mA cm−2, which is much lower than most Ni-based electrocatalysts. The overpotential of 189 mV at 100 mA cm−2 of NiFeS/NF suggests very promising OER activity for industrial applications. The electrochemically active surface area (251.25 cm2) of NiFeS/NF is obviously larger than that of NiFeS/NF (173.75 cm2) and NiFeS/NF (205.00 cm2). However, the stability of NiFeS/NF is not very good due to the intrinsic nature of metal sulfides in alkaline solution. An approach of electrodeposition of Fe hydroxide film on NiFeS/NF (NiFeS–Fe/NF) has been used to protect NiFeS/NF for better stability for the OER. The OER performances of NiFeS–Fe/NF demonstrate enhanced stability but lower activity with 101.6 mV at 10 mA cm−2. Therefore, there may be an optimal balance between activity and stability of transition metal sulfides for the OER.