Invited Paper NM-MoE2
Electrocatalysis - Ensemble versus Single Nanoparticle Investigations

Monday, December 12, 2016, 6:00 pm, Room Hau

Nanomaterials play a crucial role in catalysis thanks to their large surface-to-volume ratio and the possibility to adjust their electronic structure, i.e. reactivity. As it provides several promising routes to sustainable energy, electrocatalysis is a strongly expanding research topic to date. It provides a route to both, the production of sustainable fuels by water electrolysis or CO₂ reduction, and to their environmentally friendly utilization in hydrogen or alcohol fuel cells. The fact that these reactions occur at the solid liquid interface and that electronic and ionic charge carriers are involved, make the characterization of nano-electrocatalysts a challenging task. The overlapping effects of altered mass transport at nanoparticle modified surfaces and of changed electronic connection add to the changes in reaction kinetics. Hence, it is difficult to directly extract kinetic information from experimental data.

To overcome the obstacles of poor electronic conductivity and slow diffusional mass transport, nanomaterials are typically mixed with a conductive binder and thick films of this mixture are immobilized on rotating disc electrodes for electrocatalysis studies. However, this conventional procedure fails if porous films result or the influence of the binder material is not known. Thus, new methods for binder-free electrocatalyst characterization are being developed to enable fast and reliable electrochemical characterization of new catalyst materials. Two new approaches are presented that facility binder-free testing of electrocatalysts either using (sub-)monolayer films of nanomaterials [1] or single nanoparticle impact studies. In the first case, ensembles of nanoparticles on an electrode are produced [1], while the latter approach utilizes the Brownian motion based impacts of nanoparticles at an electrode to study their [2] electrocatalytic performance [2]. Both methodologies avoid thick films and convection. Hence, conductivity effects are minimized, while changes in the mass transport of reactants can be quantified using numerical simulations of the diffusional processes at nanoparticle modified electrodes. Accounting for these overlapping effects, the experimental electrochemical response during electrochemical reduction of CO₂, O₂ or H⁺, can be deconvoluted to reveal the true kinetic performance of novel catalysts. These methods may thus enable a more rational design and testing of new catalyst materials in the future.

References:

[1] C.C.M Neumann, E. Laborda, K. Tschulik, K.R. Ward, R.G. Compton, Nano Res. 6 (2013), 511.

[2] X. Li, C. Batchelor-McAuley, S.A.I. Whitby, K. Tschulik, L. Shao, R.G. Compton, Angew. Chem., 55, (2016) 4296.