The reduction of oxygen and protons at the interface between two immiscible electrolyte solutions (ITIES) has received a great deal of interest over the last decade, with various materials being used to catalyse these reactions. Probing the mechanisms through which these reactions proceed when using interfacial catalysts is important from both from the perspective of fundamental understanding and for catalyst optimisation. Herein, we have used interfacial-assembled graphene to probe the importance of simple electron conductivity towards the catalysis of the oxygen reduction reaction (ORR) at the ITIES, and a bipolar setup to probe the homogeneous/heterogeneous nature of the ORR proceeding through interfacial graphene. We found that interfacial graphene provides a catalytic effect towards the reduction of oxygen at the ITIES, proceeding via the heterogeneous mechanism when using a strong reducing agent.

Low-dimensional carbon materials, i.e., graphene and its functionalization with a number of semiconductor or conductor materials, such as noble metal nanostructures, have primary importance for their potential exploitation as electro-active materials, i.e., as new generation catalysts. Here, low-cost, solution chemistry-based, two-step functionalization of an individual, free-standing, chemical vapor-deposited graphene monolayer is reported, with noble metal (Au, Pt, Pd) nanoparticles to build up two-side decorated graphene-based metal nanoclusters. Either the same metal (symmetric decoration) or different metals (asymmetric decoration) are used for the preparation of bimetal graphene sandwiches, which are adsorbed at the liquid/liquid (organic/water) interface. The successful fabrication of such dual-decorated graphene-based metal nanocomposites is confirmed using various microscopic techniques (scanning electron and atomic force microscopies) and several spectroscopic methods (x-ray photoelectron, energy dispersive x-ray, mapping mode Raman spectroscopy, and electron energy loss spectroscopy). Taken together, it is inferred from these techniques that the location of deposited metal nanoparticles is on opposite sides of the graphene.

Group 6 complexes of the type [M(CO)₄(bpy)] (M=Cr, Mo, W) are capable of behaving as electrochemical catalysts for the reduction of CO₂ at potentials less negative than those for the reduction of the radical anions [M(CO)₄(bpy)]^.−. Cyclic voltammetric, chronoamperometric and UV/Vis/IR spectro-electrochemical data reveal that five-coordinate [M(CO)₃(bpy)]²⁻ are the active catalysts. The catalytic conversion is significantly more efficient in N-methyl-2-pyrrolidone (NMP) compared to tetrahydrofuran, which may reflect easier CO dissociation from 1e⁻-reduced [M(CO)₄(bpy)]^.− in the former solvent, followed by second electron transfer. The catalytic cycle may also involve [M(CO)₄(H-bpy)]⁻ formed by protonation of [M(CO)₃(bpy)]²⁻, especially in NMP. The strongly enhanced catalysis using an Au working electrode is remarkable, suggesting that surface interactions may play an important role, too.

Metal nanoparticles are readily formed, with a reasonable degree of size and shape control, using solution-based reduction methods under ambient conditions. Despite the large number of reports in this field, much of our knowledge of nanoparticle growth is largely empirical, with the relationship between particle form and growth conditions, for example, still not well understood. Many nanoparticle preparation routes actually depend on not one, but two, solution phases, i.e. the syntheses involve reaction or transfer at the liquid–liquid (organic–water) interface. This interface can be polarised electrochemically, an approach that offers promise as a route to better understanding, and ultimately control, of nanoparticle growth.