Metal electrodes have undergone extensive study for their ability to facilitate electrochemical CO2 reduction. In large part, these metals can be broken into three categories: (1) metals that only perform H2 evolution and not CO2 reduction (e.g., most transition metals), (2) metals that generate the two-electron reduced products CO or HCOOH (e.g., most p-block metals), and (3) copper, which generates highly reduced hydrocarbons. Although metals have been widely examined for CO2 reduction ability, significantly fewer bimetallic alloys have been researched for the same purpose. Moreover, the few alloy studies that have been reported suggest that one cannot expect to combine two metals and achieve the same CO2 reduction products that the two constituent metals make on their own. Therefore, one research area in the Bocarsly Lab involves (1) discovering new CO2-reducing bimetallic alloy electrocatalysts and (2) better understanding the ways in which known alloy catalysts facilitate CO2 reduction.
One example of an ongoing bimetallic alloy project within the group involves the examination of NiaGab thin film alloys as materials that facilitate electrochemical CO2 reduction. NiaGab thin films were synthesized on both highly oriented pyrolytic graphite (HOPG) and glassy carbon substrates and subsequently analyzed by powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy (below). The materials were then used in CO2-saturated bulk electrolysis experiments which demonstrated that both the CO2 reduction products generated as well as their Faradaic efficiencies were correlated with the identity of the substrate material (i.e., HOPG versus glassy carbon). This result is significant because the substrate in film-facilitated CO2 reduction is frequently regarded as an innocent bystander (i.e., the “house” for the CO2-reducing thin film catalyst) in the electrocatalysis process. In this case, however, the film plays a role during either the film synthesis or the electrochemical reduction itself.
Scanning electron microscopy images of Ni3Ga on HOPG (left) and glassy carbon (right). Despite having the same Ni-Ga composition, the films have starkly contrasting morphologies.
Research projects on bimetallic alloy CO2 reduction catalysts in the Bocarsly Lab typically result in a gained knowledge of solid state synthesis techniques (e.g., furnace use, arc melting), materials characterization methods (e.g., powder X-ray diffraction, electron microscopy), electrochemical experimentation (e.g., cyclic voltammetry, electrolysis), and product analysis methods (e.g., gas chromatography, NMR spectroscopy).