Chapter 4. Bifunctional Graphene-Based Carbocatalyst for Biomass Reforming
5.1. Introduction
Owing to unique structures and superior properties of GO, GO-based nanocomposites have emerged as an important material in the field of electrochemistry. For example, GO itself exhibits a moderate conductivity, and good chemical stability, and able to facilitate the direct electron transfer.
In addition, the hybridization of inorganic nanomaterials can offer GO-based composites novel electrocatalytic properties. In this case, GO provides an ideal platform for the deposition of metal nanoparticles due to their various functionalities and high stability of GO nanosheets. Moreover, GO can improve catalytic stability during electrochemical reaction by preventing aggregation of active metal nanomaterials.
In Chapter 5, we introduce two different modification methods including chemical functionalization of GO and LbL assembly method to hybridize graphene-based materials with diverse metal nanoparticles.
5.1.1. Carbon-Based Electrocatalysts
Among various electrochemical system, three representative reactions, including the oxygen reduction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), are critical for clean and renewable energy societies for fuel cells and water splitting process.1-2 To improve performance these reactions, novel and appropriate catalysts are required for ORR in fuel cells and OER and HER for water splitting. During past few decades, tremendous efforts have been reported to develop novel metal-based nanomaterials such as platinum (Pt), palladium (Pd), and iridium (Ir) for electrochemical reactions. However, metal-based catalysts have severe limitations such as poor stability, gas poisoning effect, and environmentally toxicity. Moreover, limited resources and high cost of noble metals make hard to commercialized applications. These limitations have increased an interest about metal-free electrocatalysts, especially carbon-based materials. In 2009, Dai et al. discovered a new type of electrocatalysts based on heteroatom-doped carbon nanomaterials as an effective, low-cost, metal-free alternative to platinum (Pt) for ORR.3 Since then, tremendous researches have been geared to utilize carbon-based electrocatalysts for various applications.4-7
5.1.2. Electro-Reforming of Biomass
Water splitting is an ideal process to produce hydrogen without any byproducts. However, it requires huge electro-energy to overcome energy barrier of anodic reaction, OER. Generally, OER needs an applied voltage more than 1.23 V to provide the thermodynamic driving force. In practice,
the electrolysis potential usually requires 1.6 and 2 V to get electrolysis current densities in the range of 1–2.0 A/cm2.8-9 Alternatively, several researches have been proposed to replace anodic OER to more easily oxidizable molecules such as methanol,10 ethanol,11-13 ammonia,14-15 and urea,16 which are referred as electrochemical reforming or electro-reforming. Since it has lower overpotential, therefore, hydrogen evolution is much more favorable when compared to water electrolysis. In addition, since O2 is valueless products after electrolysis, it is more beneficial to generate value-added chemicals after the anodic reaction.
Among easily oxidizable substrates, 5-hydroxymethylfurfural (HMF) has been classified as the top biomass-derived building block chemicals to produce valuable products.17-18 HMF has two distinct functional groups including hydroxyl and carboxylic acid group, and they can be converted into various forms with oxidation, hydrogenation, reduction, or condensation reaction. For example, 2,5-furandicarboxylic acid (FDCA), one of the products from HMF oxidation, is regarded as an important monomer to synthesize a renewable polymer, poly(ethylene furanoate) in place of petroleum-derived poly(ethylene terephthalate).17
5.1.3. Nanoarchitectonics
In order to satisfy the worldwide demands for efficient usage of materials and resources with proper applications, scientific efforts regarding synthesis of molecules of materials, fabrication of devices, or biological treatments have been continuously required. One of important keys for these efforts is precise control of structures and organization in nanoscale level to make efficient flows, and conversion of materials and energies.
In addition to developing new materials, a novel concept to fabricate architectures of functional materials and systems has been proposed as a nanoarchitectonics concept, which was initiated by Masakazu Aono.18 In addition to self-assembly processes, the nanoarchitectonics includes chemical synthesis, manipulation of atom/molecules, and field-induced materials control. However, fabrication of functional architectures in three-dimensional direction is not always easy. Direction-
5.1.4. References
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(2) Joya, K. S.; Joya, Y. F.; Ocakoglu, K.; van de Krol, R., Water-Splitting Catalysis and Solar Fuel Devices: Artificial Leaves on the Move. Angew. Chem. Int. Ed. 2013, 52, 10426-10437.
(3) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L., Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science 2009, 323, 760-764.
(4) Liu, X.; Dai, L., Carbon-Based Metal-Free Catalysts. Nat. Rev. Mater. 2016, 1, 16064.
(5) Zheng, Y.; Jiao, Y.; Zhu, Y.; Li, L. H.; Han, Y.; Chen, Y.; Du, A.; Jaroniec, M.; Qiao, S. Z., Hydrogen Evolution by a Metal-Free Electrocatalyst. Nat. Commun. 2014, 5, 3783.
(6) Qu, L.; Liu, Y.; Baek, J.-B.; Dai, L., Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells. ACS Nano 2010, 4, 1321-1326.
(7) Wang, S.; Zhang, L.; Xia, Z.; Roy, A.; Chang, D. W.; Baek, J.-B.; Dai, L., Bcn Graphene as Efficient Metal-Free Electrocatalyst for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2012, 51, 4209-4212.
(8) Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D., A Comprehensive Review on PEM Water Electrolysis. Int. J. Hydrog. Energy 2013, 38, 4901-4934.
(9) Pagliaro, M. V.; Bellini, M.; Bevilacqua, M.; Filippi, J.; Folliero, M. G.; Marchionni, A.; Miller, H.
A.; Oberhauser, W.; Caporali, S.; Innocenti, M.; Vizza, F., Carbon Supported Rh Nanoparticles for the Production of Hydrogen and Chemicals by the Electroreforming of Biomass-Derived Alcohols. RSC Adv. 2017, 7, 13971-13978.
(10) Take, T.; Tsurutani, K.; Umeda, M., Hydrogen Production by Methanol–Water Solution Electrolysis. J. Power Sources 2007, 164, 9-16.
(11) Lamy, C.; Jaubert, T.; Baranton, S.; Coutanceau, C., Clean Hydrogen Generation through the Electrocatalytic Oxidation of Ethanol in a Proton Exchange Membrane Electrolysis Cell (PEMEC):
Effect of the Nature and Structure of the Catalytic Anode. J. Power Sources 2014, 245, 927-936.
(12) Bambagioni, V.; Bevilacqua, M.; Bianchini, C.; Filippi, J.; Lavacchi, A.; Marchionni, A.; Vizza, F.; Shen, P. K., Self-Sustainable Production of Hydrogen, Chemicals, and Energy from Renewable Alcohols by Electrocatalysis. ChemSusChem 2010, 3, 851-855.
(13) Chen, Y. X.; Lavacchi, A.; Miller, H. A.; Bevilacqua, M.; Filippi, J.; Innocenti, M.; Marchionni, A.; Oberhauser, W.; Wang, L.; Vizza, F., Nanotechnology Makes Biomass Electrolysis More Energy Efficient Than Water Electrolysis. Nat. Commun. 2014, 5, 4036.
(14) Schalenbach, M.; Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D., Pressurized PEM Water Electrolysis: Efficiency And Gas Crossover. Int. J. Hydrog. Energy 2013, 38, 14921-14933.
(15) Vitse, F.; Cooper, M.; Botte, G. G., On the Use of Ammonia Electrolysis for Hydrogen Production. J. Power Sources 2005, 142, 18-26.
(16) Yan, W.; Wang, D.; Botte, G. G., Electrochemical Decomposition of Urea with Ni-Based Catalysts. Appl. Catal. B 2012, 127, 221-226.
(17) van Putten, R.-J.; van der Waal, J. C.; de Jong, E.; Rasrendra, C. B.; Heeres, H. J.; de Vries, J. G., Hydroxymethylfurfural, a Versatile Platform Chemical Made from Renewable Resources. Chem. Rev.
2013, 113, 1499-1597.
(18) Bozell, J. J.; Petersen, G. R., Technology Development for the Production of Biobased Products from Biorefinery Carbohydrates—the Us Department of Energy’s “Top 10” Revisited. Green chem.
2010, 12, 539-554.
5.2. Covalent Functionalization Based Heteroatom Doped Graphene Nanosheet for Oxygen