Direct electricity generation from cellulose without saccharification and fermentation processes was achieved on gold electrode under the alkaline conditions. We (i) overcame problems with the insolubility of cellulose, and captured its electrochemical potential, and (ii) showed that cellulose was converted to cellulose derivatives due to electrochemical oxidation. In addition, we (iii) constructed a cellulose-based fuel cell, demonstrating that cellulose can be direct electrical based fuel source. The presented fuel cell system overcomes the enormous distribution challenges encountered with other alternative bioenergy sources such as hydrogen.
The electrochemical properties of cellulose dissolved in NaOH solution at a Au surface were investigated by cyclic voltammetry, FTIR spectroscopy, the electrochemical quartz crystal microbalance technique, and electrochemical impedance spectroscopy. The reaction products were characterized by SEM, TEM, and FTIR and NMR spectroscopy. The results imply that cellulose is irreversibly oxidized. Adsorption and desorption of hydroxide ions at the Au surface during potential cycling have an important catalytic role in the reaction (e.g., approach of cellulose to the electrode surface, electron transfer, adsorption/desorption of the reaction species at the electrode surface). Moreover, two types of cellulose derivatives were obtained as products. One is a water-soluble cellulose derivative in which some hydroxyl groups are oxidized to carboxylic groups. The other derivative is a water-insoluble hybrid material composed of cellulose and Au nanoparticles (≈4 nm). Furthermore, a reaction scheme of the electrocatalytic oxidation of cellulose at a gold electrode in a basic medium is proposed.
A unique artificial catalyst that mimics the structure of active sites in real enzymes using functionalized carbon nanotubes is presented. This concept will allow for the potential construction of a library of biomimetic catalysts for enzyme active centers, for which the structure-catalysis relationships are well defined.
The recently reported electro-catalytic reaction mechanism for the oxidation of cellulose is proposed to work also for the electro-oxidation of other polysaccharides (e.g. hemicelluloses). In this report, the electrochemical reactivity of some hemicelluloses (xylan, arabinoxylan, glucomannan, xyloglucan, and glucuronoxylan) in 1.3 M NaOH solution is described. The electrochemical property of each of the studied hemicelluloses at the Au electrode surface was characterized by cyclic voltammetry. Xylan, xyloglucan and glucuronoxylan were found to be electrochemically active. Electrochemical properties of xylan were further studied by electrochemical impedance spectroscopy. The electrochemical reaction products of xylan, obtained by extensive electrolysis of the xylan solution by cyclic voltammetry, were characterized by FTIR spectroscopy, (13)C-NMR spectroscopy, SEM and TEM. The structural studies suggest that the oxidized xylan is a functional material where some of the OH-groups have been oxidized to carboxyl groups making that part of the oxidation product soluble in water under ambient conditions (23 °C, pH 7). The other part remains insoluble in water and contains Au nanoparticles. This work indicates that other polysaccharides than cellulose can also be electrochemically oxidized.
A better
understanding of cellulose–cellulose interactions
is needed in applications such as paper making and all-cellulose composites.
To date, cellulose–cellulose studies have been chemistry-oriented.
In these studies, the sample surfaces have been modified with different
chemicals and then tested under an atomic force microscope (AFM) using
a colloidal probe (CP). Studies of cellulose–cellulose interaction
based on sample morphology and mechanical properties have been rare
as a result of the complex surface structure and the soft texture
of the cellulose. The current surface interaction models, such as
the Johnson–Kendall–Roberts (JKR) model in which the
studied bodies are assumed to have smooth surfaces, can no longer
fully reveal the interfacial behavior between two cellulose surfaces.
Therefore, we propose a new type of contact model for rough–rough
interaction by dividing the surface contacts into primary and secondary
levels. The main idea of the new model is to take into account local
individual contact details between rough surfaces. The model considers
the effect of the surface topography by including the asperities and
valleys on a cellulose sphere used as the colloidal probe in imaging
the topography of a cellulose membrane (CM). In addition, the correlation
between the surface morphology and adhesion is studied. To verify
the importance of including the effect of the surface roughness in
contact analysis and validate our hypothesis on the correlation between
the surface morphology and adhesion, an extensive set of experiments
was performed. In the experiments, a combination of the AFM peak-force
mode (PFM) and the CP technique was employed to acquire a massive
amount of information on cellulose–cellulose interactions by
measuring the adhesion among six CSs of different sizes and a CM.
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