Title: Heterogeneous Electrocatalysts for Solid-state Alkaline Water Electrolyzers
Speaker: Prof. Vijay K. Ramani, Washington University in St. Louis and IIT-Delhi VAJRA Fellow
Venue: CSIR-IMMT meeting Hall
Date: 2018-Aug-21 16:00:00
Abstract: Hydrogen production by alkaline water electrolysis using hydroxide-conducting anion exchange membranes (AEMs) has seen a renewed interest as an alternative to traditional liquid alkaline water electrolyzers, proton exchange membrane (PEM) electrolyzers, and solid oxide water electrolyzers. Anion exchange membrane electrolyzers provide an efficient, modular, and reliable method to produce hydrogen from water and renewable electricity sources. One of the main benefits of anion exchange membrane electrolyzers arises from the more facile oxygen evolution reaction (OER) kinetics in alkaline environments and the concomitant possibility of employing non-platinum group (non-PGM) catalysts without suffering the stability problems common in acid media. However, a challenge that arises is the sluggish kinetics for the hydrogen evolution reaction (HER) in alkaline media.
During our research into active and stable OER catalysts for alkaline operation, electrically conducting metal oxides (eliminating the need of a conducting support for the catalyst) with the pyrochlore structure (A2B2O7-y, with A=Pb or Bi and B= Ru, Ir or Os) emerged as among the most active and stable OER catalysts. Specifically, the exceptional OER activity and stability of lead ruthenate pyrochlore catalysts was quantified using a rotating disk electrode and further evaluated in an anion exchange membrane water electrolyzer. The OER overpotentials obtained with the pyrochlore catalyst in the full cell were 0.1-0.2 V lower than for IrO2 across the entire current density range, with stable performance over hundreds of hours.
Since operation in alkaline media leads to more sluggish HER kinetics, we have evaluated ways to improve the HER activity of Pt-based electrocatalysts at high pH. Bifunctional electrocatalysts containing Pt clusters to combine the protons to form hydrogen gas, and hydrophilic domains able accelerate water dissociation were able to substantially improve HER kinetics under alkaline conditions. The hydrophilic moieties that help the water splitting are varied. We have investigated nickel hydroxide and ruthenium oxide as co-catalysts together with Pt. The bi-functional catalysts were evaluated in an anion-exchange membrane water electrolyzer operated with ultrapure water, and outperformed Pt/C by about 0.15 V across the entire current density range. Similarly, electrolyzer experiments showed that Pt/C/10%Ni(OH)2 performs as well as Pt/C with only half the Pt loading. We have also demonstrated enhanced HER activity in a Pt electrocatalyst deposited onto a mixed-metal-oxide support composed of titanium dioxide (TiO2) and ruthenium dioxide (RuO2).
This presentation will elaborate on both the OER and HER electrocatalysis in alkaline media, and will provide specific examples of successfully translated electrocatalysts. A brief overview of other ongoing projects will also be presented.
