The electrochemical interconversion of small molecules containing C, O, N, and H is at the core of energy and environmental chemistry. Research in the McCrory Lab generally focuses on using careful electroanalytical studies to elucidate the mechanism of electrocatalytic systems, then using this mechanistic understanding to inform the rational design of next-generation catalyst materials. We are broadly interested in the electrochemical interconversion of small molecules relevant to energy and environmental chemistry. For instance, we are particularly interested in the selective electrochemical reduction of CO2 via the CO2 reduction reaction (CO2RR) due to its applications towards both storing energy from intermittent energy sources in the form of chemical bonds (e.g. solar fuels) and as a pathway to converting CO2 in industrial waste streams to value added products. Another reaction of major interest is the electrochemical reduction of NO3– salts to NH3 or N2 as a means of remediating agricultural and industrial wastewater. We are also interested in the oxidation of water to O2 in the oxygen evolution reaction (OER), the oxidative half reaction that occurs at the anode in solar fuels devices, and the selective oxidation of alcohols in the alcohol oxidation reaction (AOR) for electrosynthetic applications.
In the McCrory group, our general research approach is to develop enabling technologies that allow for the careful study and control of electrocatalytic processes with an emphasis on kinetic and mechanistic analysis, and to use these approaches to address fundamental challenges in the electrochemical conversion of small molecules by solid-state and molecular catalysts. We use a combination of surface science and electrochemistry to directly observe reactive intermediates in the catalytic pathway in model systems and then use these mechanistic findings to develop new, efficient electrocatalytic materials. A few key projects in our group are discussed below.
Controlling Coordination Environment through Polymer Encapsulation
Encapsulating molecular electrocatalysts within coordinating polymers allows us to control the catalysts’ chemical microenvironments and promote higher activity and selectivity for electrochemical conversions. This approach is inspired by biological systems where fast catalytic activity and high reaction selectivity are achieved in enzymes through optimization of the primary, secondary, and outer coordination spheres of the enzymes’ active sites.
In particular, we have shown that immobilizing cobalt phthalocyanine (CoPc) inside of poly-4-vinylpyridine (P4VP) polymer films results in suppression of the competitive hydrogen evolution reaction and promotes the low overpotential reduction of CO2 to CO. The encapsulating polymer alters the catalyst’s primary, secondary, and outer coordination spheres synergistically to promote increased activity and selectivity for CO2 reduction. Our work focuses on understanding the fundamental mechanisms and kinetics of charge and substrate transport in these systems, and how this influences overall reaction activity and selectivity.
Developing Reductively Stable Self-Assembled Monolayers on Metallic Surfaces
We are developing new ways to immobilize molecular electrocatalysts onto reflective metal electrode surfaces using well defined self-assembled monolayers (SAMs) that are stable under electrocatalytic conditions. Immobilization of catalysts via stable, well-defined SAMs allows for careful and unambiguous studies of electrocatalytic processes as a function of the rates of substrate and electron delivery, and allows in situ spectroscopic characterization of the reactive species and catalytic intermediates using reflective IR spectroscopy techniques. However, common Au-thiol SAMs show poor reductive stability, preventing their use to tether molecular catalysts for reactions like the electrochemical CO2 reduction reaction (CO2RR) and the nitrate reduction reaction (NO3RR). Our preliminary work has focused on developing new approaches for quantifying electrochemical reductive desorption of SAMs on metal surfaces, specifically non-Au metal surfaces for which desorption cannot be estimated from simple voltammetric techniques. A large component of our current and future studies is using in situ grazing angle XAS and XES as a function of applied electrochemical potential to observe the mechanism of reductive desorption.
Molecular Electrocatalysis: Discrete Catalysts to Multidimensional Architectures
For most molecular electrocatalysts, introducing ligand modifications that shift the catalysts’ redox potentials more positive leads to a decrease in the metal site nucleophilicity, and in turn decreases the catalysts’ ability to coordinate and reduce CO2. This correlation between a catalyst’s redox potential, which governs catalytic onset, and nucleophilicity of the catalyst’s metal site leads to typical molecular scaling relationships: beneficial decreases in effective overpotential, the extra energy beyond the thermodynamic requirement needed to drive the reaction, are typically correlated with detrimental decreases in catalytic activity. Our work focuses on developing systems that break molecular scaling relationships that allow for the simultaneous minimization of overpotential and maximization of catalytic activity. Our approach is to design complexes with redox-active ligands where catalytic onset immediately follows ligand reduction, thus partially decoupling catalytic onset and effective overpotential from the nucleophilicity of the metal sites. We are also focused on incorporating molecular catalyst systems into macromolecular structures and understanding how this changes the kinetics and mechanisms of electrocatalytic transformations.
Role of Metal Dopants in Heterogeneous Electrocatalysts
Our group is interested in understanding the role of dopants, both intentional and unintentional, on electrocatalytic activity and product distributions for the oxygen evolution reaction (OER) and the CO2 reduction reaction (CO2RR). Much of our work has focused on designing new Co3-xMxO4 spinel materials for the OER, where M is an early transition metal. In particular, we have explored how the incorporation of different metals into the lattice influences catalytic activity and stability for the OER. Moving forward, we are focused on expanding this work to understand how changing the composition and structure of Co3-xMxO4 spinel materials influence activity for other oxidative reactions such as selective alcohol oxidation.
Our other efforts have focused on quantifying the influence of trace-metal contaminants such as Ag+ from reference electrodes on CO2RR product distributions at Cu electrodes.