REVISED - Integrated Harvesting and Storage of Oxygen from Seawater Using Efficient Bipolar Membrane Electrolysis, Impurity Tolerant Electrocatalysts, and Designer Metal Organic Frameworks
Abstract
The objective of this multi-disciplinary university research initiative is to develop the fundamental science behind the direct generation and integrated storage of oxygen gas from unpurified seawater. Previous work on seawater electrolysis has used buffered near-neutral or alkaline electrolytes where reaction thermodynamics favors the formation of oxygen gas over the more kinetically facile chloride oxidation. These approaches, however, are not suited for thisapplication because they are not compatible with the solid-polymer ion-conducting membranes that are essential to separate the evolved hydrogen and oxygen gas and allow anode and cathode operation at differential pressure. With buffered seawater electrolytes, pH gradients form and lead to poor performance as buffer ions do not transport effectively. If alkaline anion-exchange membranes are used, chloride-ion transport contributes substantially to the ionic current, alsoleading to pH gradients, acidification at the anode, and eventual evolution of toxic chlorine gas. If acidic cation-exchange-membrane electrolyzers are used, sodium cations exchange for protons, badly hindering performance, and the locally acidic conditions preference chlorine production.We will study a fundamentally new approach for seawater electrolysis that uses bipolar membranes (BPMs) to separate the anode and cathode to address the challenges associated with existing methods. The BPMs will consist of a hydroxide-conducting membrane, a protonconducting membrane, and an intervening layer of water-dissociation catalyst. The BPM conducts ionic current by dissociating water and selectively transporting hydroxide to the anode and protons to the cathode. The BPM approach supports electrochemical compression of the output oxygen for storage in a lightweight MOF-filled tank, essentially eliminates crossover/mixing of the oxygen and hydrogen gas, and prevents chloride from reaching the anode (which is nonetheless maintainedat an alkaline local pH where oxygen evolution occurs preferentially over chlorine).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 08, 2020
- Source ID
- N000142012517
Entities
People
- Shannon W. Boettcher
Organizations
- Office of Naval Research
- United States Navy
- University of Oregon