Abstract
Extensive use of fossil fuels can lead to energy depletion and serious environmental pollution. Therefore, it is necessary to solve these problems by developing clean energy. Graphene materials own the advantages of high electrocatalytic activity, high conductivity, excellent mechanical strength, strong flexibility, large specific surface area and light weight, thus giving the potential to store electric charge, ions or hydrogen. Graphene-based nanocomposites have become new research hotspots in the field of energy storage and conversion, such as in fuel cells, lithium-ion batteries, solar cells and thermoelectric conversion. Graphene as a catalyst carrier of hydrogen fuel cells has been further modified to obtain higher and more uniform metal dispersion, hence improving the electrocatalyst activity. Moreover, it can complement the network of electroactive materials to buffer the change of electrode volume and prevent the breakage and aggregation of electrode materials, and graphene oxide is also used as a cheap and sustainable proton exchange membrane. In lithium-ion batteries, substituting heteroatoms for carbon atoms in graphene composite electrodes can produce defects on the graphitized surface which have a good reversible specific capacity and increased energy and power densities. In solar cells, the performance of the interface and junction is enhanced by using a few layers of graphene-based composites and more electron-hole pairs are collected; therefore, the conversion efficiency is increased. Graphene has a high Seebeck coefficient, and therefore, it is a potential thermoelectric material. In this paper, we review the latest progress in the synthesis, characterization, evaluation and properties of graphene-based composites and their practical applications in fuel cells, lithium-ion batteries, solar cells and thermoelectric conversion.
Highlights
Green energy is called clean energy, including solar energy, wind energy, water energy, tidal energy, geothermal energy and biomass power, whereas fossil fuels are nonrenewable energy sources, including coal, crude oil, natural gas, oil shale, oil sand and combustible ice under the sea [1,2]
We review the progress in their applications in green energy materials, e.g., replacing precious metal materials as catalysts in hydrogen fuel cells, Crystals 2021, 11, 47 increasing the cycle stability and competitive rate performance as electrode materials in lithium-ion batteries and enhancing power conversion efficiency in solar cells and thermoelectric conversion
Organic photovoltaic (OPV) cells use photosensitive organics as semiconductor masolar cells was due to the oxidation-induced p-type self-doping of the graphene-silicon terials and generate voltage to form current through the photovoltaic effect [129]
Summary
Green energy is called clean energy, including solar energy, wind energy, water energy, tidal energy, geothermal energy and biomass power, whereas fossil fuels are nonrenewable energy sources, including coal, crude oil, natural gas, oil shale, oil sand and combustible ice under the sea [1,2]. In order to tackle the above problems, graphenebased nanocomposites with unique properties are studied extensively for their potential applications in clean energy-related areas, e.g., hydrogen fuel cells, lithium-ion batteries, solar cells, thermoelectric conversion and other environmental and energy fields. Doping heteroatoms (nitrogen, boron and phosphorus) into the graphene carbon lattice in Li-ion batteries can effectively customize the properties of pristine graphene such as semiconductor properties, surface reactivity, electronic properties, band structure and magnetic properties [9,10] These advantages enable LIBs to have good reversible specific capacity, rate capability, high capacity retention capacity and improved charging speed. We review the progress in their applications in green energy materials, e.g., replacing precious metal materials as catalysts in hydrogen fuel cells, Crystals 2021, 11, 47 increasing the cycle stability and competitive rate performance as electrode materials in lithium-ion batteries and enhancing power conversion efficiency in solar cells and thermoelectric conversion. We use mathematical models to evaluate these applications and point out the current problems and future research directions in this field
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