Functional Carbon Materials Derived from Metal-Organic Frameworks (MOFs) for Electrochemical Energy Storage and Coversion

Abstract

World electricity demand is estimated to double by the mid-century and to triple by the end of the century, even after efficient conservation technology development. Fossil fuels such as natural gas and oil, the major contributors to global electricity generation, are anticipated to peak-over in the following few decades. The generation of electrical energy from renewable resources instead of from fossil fuels has received great interest due to the resource limitations and environmental impacts of the latter. Renewables such as solar radiation and wind face significant challenges of time-dependent intensity fluctuation and natural geographical distribution. Among the different strategies for smoothing the disordered renewables, the electrical energy storage and conversion has been recognized the most efficient and effective approach. Energy storage in the form of charges include supercapacitors and battery technologies, the former is very effective in terms of power density while the latter is the best option in terms of energy density. Energy conversion devices include fuel cells, which can generate electricity from chemical fuels with large efficiency and zero pollutant emission and are very suitable for use in vehicle engines and portable electronics. In the first part of this research work, different MOFs precursors, namely MOF-5, Zn-BTC, MOF-199, MIL-101(Cr) and ZIF-12 are converted to pure carbon, and metal oxide decorated carbon structures by the inert-atmosphere template carbonization approach. MOF-derived carbon nanospheres and microporous carbons have delivered specific capacitance in the range of 150 to 350 F g–1, the optimum performance of the designed electrode materials in comparison to the literature. In long-term cycling performance, the copper oxide decorated graphitic carbons and the chromium oxide decorated turbostratic graphitic carbons retained about 95% of their initial capacitance. The novel innovative hybrid composite of cobalt oxide embedded N-doped carbon nanotubes (CNTs) from single-step calcination of ZIF-12 has shown an excellent lithium charge/discharge and storage, retaining ~95% capacity after 50 cycles and a reversible capacity of ~1100 mA h g–1 at a current density of 0.1 A g–1, which far exceeds the performance of conventional lithium ion battery anode materials under similar conditions. In the second part of this research work, platinum group metal-type (PGM-type) catalysts were deposited on MOF-5-derived high-surface area carbon and electrochemically evaluated for the fuel cell cathodic sluggish oxygen reduction reaction (ORR). The Pt-Ni composition (1:1) exhibited a pronounced positive shift of 90 mV in onset-potential while the Pt-Cu composition (1:1) has delivered an outstanding stability and longevity when evaluated against the commercial Pt/C (20%) catalyst. The significantly improved activity and stability of the catalysts can be attributed to the Pt electron interaction with first-row transition metals and carbon support that prevents the nanoparticles from agglomeration and dissolution as has been proved in X-ray and microscopic analysis.