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MSc assignment: Alternative platinum electrodes for Kolbe electrolysis

MSc. Assignment: Alternative platinum electrodes for Kolbe electrolysis

Photocatalytic Synthesis (PCS) and Biomass Technology Group (BTG)

Chair: Prof. Dr. Guido Mul
Supervisors: Talal Ashraf and Margot Olde Nordkamp

Introduction 

Pyrolysis oil derived from biomass can be an alternative fuel to contribute to the energy transition. However, raw oil is highly acidic, therefore to increase the quality upgrading technologies are required. Yet, existing upgrading technologies are energy-intensive and suffer from catalyst degradation.

Electrochemical techniques (schematically represented in Figure 1) can provide a sustainable possibility to stabilize and convert the oil at moderate reaction conditions. One way to remove the acids is by selective oxidation at the anode. In this selective oxidation, carboxylic acids are converted in a so-called Kolbe oxidation to form alkanes and carbon dioxide gas (reaction 1). The protons and electrons generated at the anode can be applied to reduce protons to hydrogen gas (reaction 2) or reduce aldehydes or ketones to alcohols (reaction 3).

Figure 1. Electrochemical cell with conversion of aldehydes/ketones to alcohol at the cathode and conversion of carboxylic acids to alkane and carbon dioxide at the anode.

Project description and goal

Using model components in aqueous solution or the water fraction of the pyrolysis oil, reaction mechanisms can be further understood, and product yields and selectivity determined and optimized. Catalysts/electrode composition as well as operating conditions can be changed readily.
Despite the emerging interest in Kolbe electrolysis, electrode design is barely explored. Platinum is one of the most common electrode materials used for Kolbe electrolysis. So far, research has primarily focused on the use of platinum foil for Kolbe electrolysis. However, the use of platinum offers challenges. Firstly, it is very expensive, and moreover, it seems that platinum in different structures promote different reaction pathways than the Kolbe reaction pathway, like the non-Kolbe pathway.  Alternatives for the platinum foil are ‘platinum black’, different facet structures, or platinum deposited on substrates such as on carbon or alumina/silica.

The goal of this research is to investigate the effect of the platinum surface/geometry and substrate material on the product yield/selectivity. Additionally, the stability of these synthesized electrodes will be explored. It is relevant to understand how platinum promotes the Kolbe reaction, and how platinum can be used in a cost-effective way. At industrially relevant conditions and scale, the use of Pt might significantly increase the capital costs of the process. An example of increasing the effective reaction area of platinum is by using/producing nanoparticles or nanofilms and depositing these on the substrate.

Skills

  • Preparation of the of the platinum electrodes
  • Surface characterization of the electrodes using e.g. XRD and SEM
  • Electrochemical characterization of the performance and stability of the electrodes

References

(1)    Schäfer, H. J. (1990). Recent contributions of Kolbe electrolysis to organic synthesis. In Electrochemistry IV (pp. 91-151). Springer, Berlin, Heidelberg.

(2)   Neubert, K., Schmidt, M., & Harnisch, F. (2021). Platinized Titanium as Alternative Cost‐Effective Anode for Efficient Kolbe Electrolysis in Aqueous Electrolyte Solutions. ChemSusChem, 14(15), 3097.