Synthesis, Characterization and Evaluation of Binary Alloys for Electrochemical Carbon Dioxide Reduction

Mitigation of carbon dioxide emissions is one of the greatest challenges facing mankind [1]. A range of different technical approaches will be needed to reduce CO2 emissions and associated negative effects, because of the scale of the problem, and different technologies might be more appropriate in different scenarios, depending on industry, location and other constraints [2]. Currently, renewable fuels are produced predominantly from biomass. Electrochemical reduction of CO2 has the potential to enable industrial scale production of fuels by storing renewable electricity in chemical bonds [3,4].

Polycrystalline and single crystal metal surfaces have been studied extensively with the aim of understanding reaction mechanisms and achieving high energy efficiency and catalytic activity [5,6]. Nearly all polycrystalline metals suffer from low energy efficiency and stability, while their nano-structured counterparts perform usually much better in terms of both activity and selectivity [7]. However, lowering the onset potentials of energy dense products such as hydrocarbons and alcohols is not achieved so far because the binding strength of the key intermediates cannot be tuned without effecting the others, i.e. scaling relationships [8]. On the other hand, alloys might break these relationships by introduction of electronic and more importantly geometric effects [9].

Alloys are attracting attention starting from very early CO2 electroreduction research [5,10]. Recently with the discovery of superior activity of nano-structured metal electrodes, alloy nano-particles are currently at the centre of interest in many research groups [11-16]. Copper is still the only metal capable of producing hydrocarbons (mostly methane and ethylene) and alcohols with 'reasonable selectivity'. Thus many efforts have been made to further control the activity and selectivity by alloying copper. However, alloying copper always lowers the production of hydrocarbons as the alloys become enriched by the foreign atom [11,17,18]. Ethylene formation specifically requires square arrangement of copper atoms on Cu(100) surface while the steps and defects or an existence of a foreign atom most likely has detrimental effects [19.20]. On the other hand, methane formation is considered to be enhanced on Cu(211) steps, while existence of a foreign atom might be beneficial for geometrical stabilization and breaking the scaling relationships to further lower the onset potential and increase the energy efficiency.

In this project, alloys of coinage metals (Cu, Ag, Au) will be prepared with different methods such as electrodeposition, wet chemical synthesis, solid state synthesis etc. The primary aim is to synthesize solid solutions or intermetallic compounds of metals, which have different CO and H+ binding energies. The prepared alloys will be analyzed extensively using crystallographic, spectroscopic and electrochemical methods. Finally, the performance of the alloys will be evaluated in CO2 electro-reduction by using electrochemical and chromatographic methods.

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