(399e) Low Energy Electrochemical Oxidation of Waste Lignin on Non-Precious PbO2/MWNTs Electrocatalyst for Simultaneous Generation of Value-Added Chemicals and Hydrogen

After cellulose, lignin is the most abundant and renewable terrestrial carbon resource. Its natural polymeric structure includes highly functionalized aromatic macromolecules crosslinked by inter-unit linkages (e.g. c-c and β-o-4 bonds). Interestingly, it has high content of hydrogen in its complex structure as well [1]. These exclusive features lead to valorization of lignin as a renewable alternative feedstock for production of value-added aromatic chemicals (e.g. phenols, aldehydes and ketones) and co-generation of pure hydrogen within the depletion of fossil fuel resources. However, more than 97% of lignin produced in biorefinery and paper industry are either discharged to the environment or burned to generate low-grade fuel and only small amounts of lignin are commercially used [2]. Electrochemical pathway can lead to selective depolymerization of lignin macromolecules into low molecular weight aromatics (LMWAs) [3]. In particular, electrochemical oxidation of lignin is an eco-friendly and energy-efficient process that allows us to efficiently break lignin at ambient temperature and atmospheric pressure without using expensive additives and toxic solvents due to its simple electron transfer mechanism [4]. Therefore, capital and operating costs for oxidation of lignin might be reduced compared to other catalytic oxidative processes in lignin depolymerization.

An appropriate approach for selective depolymerization of lignin is to develop nano-scale electrocatalysts that are extremely active and have high surface area. With high surface area, lignin macromolecules will likely possess better interaction and might prevent formation of lignin intermediates on the electrocatalyst surface. With this in mind, one possible electrocatalyst is lead dioxide (PbO₂); this material has high electrical conductivity, high oxygen overpotential and chemical inertness and exhibits outstanding electrochemical activity [5]. In this work, the non-precious PbO₂/MWNTs electrocatalysts were developed through successive synthesis of PbO₂ nanoparticles by hydrolysis of lead (IV) acetate [6] and further deposition of as-prepared nanoparticles on multi-walled nanotubes (MWNTs) as the support [7]. To study the kinetics, electrocatalytic activity and stability of as-prepared electrocatalyst, electrochemical oxidation of lignin was carried out in a conventional three-electrode cell. The optimum composition of PbO₂/MWNTs electrocatalyst was determined considering applied potential and final yield of LMWAs in this system.

References:

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