Structure-Activity in Electrocatalysis

We look for the fundamental properties that govern electrochemical behavior: reactivity, selectivity, conductivity and mass transport.

In a fuel cell, carbon materials, for example, are wonderful precious metal-free electrocatalysts. In the alkaline oxygen reduction reaction (ORR), for example, many carbons compete successfully with the best platinum catalysts. Their high porosity exposes many active sites, yet creates a tortuous pathway through which reagents (O2) and products (OH) cannot diffuse fast enough. To this end, many seek “hierarchically” porous carbon, containing a random combination of micropores (for maximum active site exposure) with meso- and macro-pores, for improved flow.

Hierarchical porosity is hard to produce. The ‘brute force’ method involves multi-step templating, yielding well-designed yet expensive structures. At the other extreme, the ‘serendipitous’ approach relies on pyrolyzing various biomass types (from bacteria to mammals), occasionally stumbling on excellent electrocatalysts. We seek the golden path: starting from simple and well-crafted precursors and/or templates, and driving towards full control of structure, composition, and activity.

To design hierarchical porosity, we explore the concept of Self-Templating. We prepare simple, yet precisely-tailored metal coordination polymers (MOCPs), and use these as all-in-one pyrolysis precursors towards carbon. The MOCP structures include both self-templating elements (metals for forming embedded nanoparticles) and all chemical components of the ultimate carbon (C, N, O, P…). We explore earth-abundant, little understood templating elements such as alkaline earth metals, rare earth metals, and their combinations with transition metals. By careful design of the MOCP structure and synthetic conditions, we obtain excellent ORR electrocatalysts with high degree of functional control.

We further explore unprecedented classes of carbon porosities, based on dendritic and highly-tunable templating. Our dream is to go beyond classical ‘hierarchical’ porosity, towards full interconnectivity, directionality, and tunability of pores.

In non-carbon research projects, we try to understand how doping and crystallinity affect hydroxide and oxy-hydroxide anode electrocatalysts.