Electrocatalytic generation of oxygen through metal-free organic macrocycles
Abstract
Naval operations require overcoming challenges associated with the inhospitable conditions in the oceans. Ocean waters contain large amounts of dissolved salts, gases and organic matter, as well as rapidly changing pressure and light conditions that overall make it a challenging environment for human activity. While the vastness of the marine ecosystems, and the variety of life organisms provide proof that efficient performance under the ocean is possible, many challenges are still evident for optimal human operations. Supporting human respiration underwater as well as oxygen availability are some of the main challenges. While water may be a massive source of oxygen, water splitting to yield oxygen gas is a chemistry challenge yet to be overcome. Water electrolysis proceeds via two separate half reactions, which correspond to thehydrogen evolution reaction (HER) and oxygen evolution reaction (OER)1. Splitting water to generate hydrogen and oxygen gases is a thermodynamically and kinetically challenging process with a ~G of +237 kJ mol~1 and a high overpotential loss due to the formation of high-energy intermediates1,2. More specifically, most of the lack of efficiency during water electrolysis originates from the oxygen evolution reaction (OER) process because it requires the transfer of four electrons and four protons3,4. Thus, improving OER efficiency by finding catalysts that lower the energy penalty or overpotential is an appropriate route to attack one issue of this problem in question5,6. The present proposal seeks to explore the basic science behind oxygen evolution from ocean water electrolysis through the screening of a variety of molecular, 2D and 3D materials that have been shown as promising OER catalysts. Different strategies will bedeveloped to enhance selectivity towards oxygen evolution, and stability of electrodes in simulated sea waters. Our specific aims are:Aim 1: Oxygen evolving porphyrin-based electrocatalysts. The selective generation of molecular oxygen from seawater will be explored through different oxygen evolution catalysts based on porphyrins and porphyrinoid organic macrocycles. Molecular and polymeric metallated and metal-free macrocycles will be probed electrochemically for OER activity. OER mechanisms in seawater will be investigated by using rationally designed molecular systems in bothheterogeneous and homogeneous electrochemical water-splitting environments. The understanding of the reaction pathways will aid the further improvement of such electrocatalysts. We will test the efficiency and oxygen selectivity of OER catalysts in weak alkaline environments that mimic ocean water conditions.Aim 2: Development of platform-supported porphyrinoid-based water splittingelectrocatalysts for enhanced anode contact. The stability, efficiency, and electrical conductivity of molecular and polymeric systems that perform sea water electrolysis will be enhanced by supporting them unto two and three dimensional materials such as: MoS2, MoO3, graphene oxide (GO), metal-organic frameworks (MOFs), and zeolitic immidazolate frameworks (ZIFs) and the enhancement of their electrochemical properties will be investigated. In addition we will examine the enhancement of electrocatalytic efficiency and anode stability by the self-assembly of porphyrinoid materials conducting electrodes such as MOFs@FTO, carbon paper, and titanium foil. Prior work has shown that electrodeposited molecular catalyst unto the surface of conducting electrodes enhances their stability and improves upon the Faradaic efficiency ofwater electrolysis.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 13, 2019
- Source ID
- N000141912467
Entities
People
- Dino Villagrán
Organizations
- Office of Naval Research
- United States Navy
- University of Texas at El Paso