Rational Design of Precisely Tailored Electrocatalysts for Efficient and Durable Electrocatalytic Devices
Due to their superior conversion efficiency, high power density, and green nature, sustainable energy technologies such as Fuel cells and Zinc-air batteries, once installed to produce green hydrogen fuel as well as energy storage devices, are expected to play an essential role in reducing the environmental effect of human transportation by replacing fossil fuels. However, the current bottleneck for the low-temperature polymer membrane fuel cells that dominate the fuel cell vehicle market is the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode. The slow ORR kinetics significantly reduce the efficiency of chemical→electrical energy conversion. Similarly, hydrogen production (to be used in the anode of fuel cells) through water splitting in electrolyzers also suffers from the inferior kinetics of oxygen evolution reaction (OER). The same kinetic limits exist in Zinc-air batteries, where ORR and OER are critical for their charging and recharging cycles. Typically, devices utilize catalysts to increase the reaction kinetics, and Pt/C and other platinum-group-metal (PGM) catalysts are the current benchmarks for oxygen electrocatalysis. However, using expensive and low-abundance noble metals decreases the commercial viability of electrochemical energy systems. Moreover, current benchmark catalysts also suffer voltage-dependent area loss, poor methanol tolerance, and CO poisoning, limiting their applicability. Therefore, it is critical to discover durable, abundant, active, and inexpensive catalysts that are PGM or noble metal-free. While dedicated efforts lead to many novel catalyst systems with considerable efficacies, most of the catalysts still lag behind the benchmarks and hence fail to achieve the performance targets the U.S. Department of Energy (DOE) set for low-temperature fuel cells and Zinc-air batteries. Due to the large surface area and programmable structure, chemically synthesized nanosystems, molecular materials, and network systems emerged as the front runners to replace benchmark catalysts. Despite progress, the activities of such alternate candidates still lag behind the benchmarks, and significant advancements are necessary before such catalysts can be commercially applied. Thus, the thesis focuses on formulating novel PGM-free ORR and OER catalysts that can rival benchmark PGM catalysts utilizing the fundamental chemical approaches. We hypothesize that chemical tailoring the electronic distribution and density of states of the active sites in nanomaterials, molecular systems, and metal-organic frameworks can lead to superior electrocatalytic activity by optimizing the adsorption-desorption energy of key intermediates. We test and prove the validity of our hypothesis in pristine systems, heterostructures, and on free-standing electrodes. We also investigate the effect of superior electrocatalytic activity on the performance of Fuel cells and Zn-air batteries that employ our developed catalysts as the electrodes and compare their performance to devices that use benchmarks to illustrate their superiority. Further, we unravel the fundamentals behind the observed activities through a comprehensive and highly symbiotic experimental-theoretical exploration of the processes. The thesis is divided into four chapters based on the systems investigated and the reactions explored.
Chemistry|Energy|Environmental engineering|High Temperature Physics|Alternative Energy
Noufal, Mohamed Fathi Ali Sanad, "Rational Design of Precisely Tailored Electrocatalysts for Efficient and Durable Electrocatalytic Devices" (2022). ETD Collection for University of Texas, El Paso. AAI29995612.