Interfacial Effect Study of Alkaline Membrane Media Using Microelectrodes

Tuesday, 30 May 2017
Grand Ballroom (Hilton New Orleans Riverside)
J. Malley, H. Doan, I. Gunasekara, and S. Mukerjee (Northeastern University)
Interfacial issues at anion exchange membranes greatly influence the electrocatalysis at high pH environment especially in conjunction with an anion exchange membrane. In this context it is well known that carbonate ions in the context of a prototypical anion exchange membrane such as A 201 (Tokuyama, Japan) are strongly adsorbing anions and thus can suppress HOR kinetics. Not only can carbonate ions block catalyst active sites, but they can also lower the amount of hydroxyl ions for adsorption at low pH. Moreover, corresponding ionomers such as AS-4 (Tokuyama, Japan) has a negative effect on HOR activity in the context of Pt, as shown in Figure 1c. At NUCRET, we successfully concluded the effect of carbonates in conjunction of anion exchange membrane as well as the role of corresponding ionomers such as AS-4. In this study we further extend this investigation by including microelectrodes in two different media - carbonate and hydroxide - for HER (Pt microelectrode) and OER (Ir microelectrode). Hence this presentation will include the following work:

Using A 201 in hydroxide form and carbonate form in the Solid State Cell setup (Figure 1a), under the following scenarios:

1) Water fed vs. KOH vs.K2COcontinuous feed (for electrolytes, equal conductivity and equal pH conditions);

2) HER/HOR and OER/ORR while feeding electrolyte from the top, bottom, or both.

This study is aimed at understanding the improvements observed when feeding a low concentration of carbonate at the anode interface (OER electrode) during water electropysis (Figure 1b). We hypothesize that the improvement could be because of the conductivity boost from 1% carbonate, because of different reaction mechanisms between HER (cathode side) and OER, or both. This micro-electrode study therefore is designed to not only mimic carbonate vs. hydroxide at the membrane interface via directional feed of carbonate ions (i.e., top where the microelectrode is at an interface with the membrane) or bottom to mimic mass transport and kinetics at the membrane interface. Transferring this study to the practical water splitting cell, will provide a thorough insight of the reactions between the catalyst layer and the membrane while feeding water vs. different electrolytes. It is particularly important to note that A-201 standard (Tokuyama, Japan) represents the state-of-the-art in alkaline membranes. Currently, our partner - Proton On-Site provides the full cell scale-up water splitting stack with the use of our best non-PGM catalysts for HER (60% Ni-Cr/C) and OER (40% Ni-Fe/Raney-PANI), as well as feeding 1% carbonate on the anode side.