Durable Fuel Cell Electrocatalysts for Energy Conversion

Download or read book Durable Fuel Cell Electrocatalysts for Energy Conversion written by Zishuai Zhang and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Electrocatalysts play an important avenue in clean and efficient energy conversion. Of the many electrocatalytic processes, the oxygen reduction reaction (ORR) attracts increasing attention due to its widespread importance in electrochemical cells. One of the most important applications is in proton-exchange membrane fuel cells (PEMFCs), which are considered as a promising power generation system because of its low operating temperature (70-90 ̊C), sustainable energy sources (hydrogen) and high energy efficiency. ORR is a key half reaction that takes place at the cathode with sluggish kinetics and requires noble metal (e.g. platinum)-based electrocatalysts to increase the reaction rate to attain practically usable levels. High cost and poor durability are major drawbacks of the commercial platinum on carbon (Pt/C) catalyst, and the corrosion of the carbon supports is considered one of the main reasons for the loss of expensive Pt, resulting in loss of performance of PEMFC. Therefore, more corrosion resistant, electrochemically stable and low-cost supports are highly desired for PEMFCs’ improved performance.Methanol oxidation reaction (MOR) is an anodic half reaction occurs at anodes of methanol fuel cells. Pt/C catalyst is also commonly used for that reaction. This thesis attempts to rationally design and synthesize various different nanostructured alternatives to carbon black for ORR and MOR. Graphene, a high conductive and stable two-dimensional carbon support, was successfully exfoliated electrochemically with little defects. Platinum (Pt) nanoparticles were deposited on graphene via double-pulse deposition technique. The catalyst was demonstrated to be highly efficient for MOR with a 920 mA/mg forward current density.Durable carbon nanotube (CNT) microspheres were synthesized through a facile and scalable ultrasonic bonding method without any binder or surfactant. The CNT microspheres with electrodeposited Pt were showcased as efficient ORR catalyst supports which showed no degradation after 12, 000 cycles (26.6 h). Furthermore, a soluble acicular calcium carbonate (aragonite, diameter 100 nm; length 800 nm) was used to created connected porosity in the microspheres to improve the mass transfer as the thickness increases. As for the ORR catalysis performance, the Pt decorated microspheres with macropores was 3.4 times higher (specific activity at 0.9V vs RHE) than non-macroporous microspheres with the identical Pt loading.Besides carbon-based supports, TiC was investigated as a potential carbon alternative due to its metallic electrical conductivity and excellent corrosion resistance. A cobalt oxide shell with high ORR activity was deposited onto TiC to improve its stability at high potential. We demonstrated that the oxide anchored Pt on TiC catalysts exhibited excellent durability (~100% catalytic activity remained at 0.1M KOH, and ~92% catalytic activity remained at 0.1M HClO4 after 16.7 h) compared to the Pt/C (~50% remained in both alkaline and acidic solutions). As assessed by transmission electron microscope (TEM), no significant Pt detachment or agglomeration was observed in oxide anchored catalysts, while heavily agglomeration has occurred to Pt/C.Hematene, two-dimensional layer of hematite (Fe2O3), has recently been exfoliated by means of liquid exfoliation. As the biodegradable metal, Fe-based materials attracts lots of attentions due to their ability to be entirely dissolved and cleared from the body. Electronics comprised of biodegradable metals can be programmed to degrade after the implantation. Here, we fabricated potentially biodegradable electrodes by using Au and hematene for glucose oxidation. It showed 9.5 mA/mgAu oxidation current density at the potential of 0.6V (vs. RHE), and high stability during the continuous cell cycling. Additionally, the prepared catalyst exhibited short response time and linear calibration range"--