The hydrogen evolution reaction (HER, 2 H+ + 2 e− → H2) is the cathodic reaction in electrochemical water splitting. The HER is a classic example of a two-electron transfer reaction with one catalytic intermediate, and offers the potential to produce H2, a critical chemical reagent and fuel. Driving the HER with renewable sources of energy can lead to a sustainable source of hydrogen fuel that can stored, transported and used in a zero-emission fuel cell of combustion engine. Achieving high energetic efficiency for water splitting requires the use of a catalyst to minimize the overpotential necessary to drive the HER. Platinum is the best known catalyst for HER and requires very small overpotentials even at high reaction rates in acidic solutions. However, the scarcity and high cost of Pt limits its widespread technological use. We study the fundamental material properties that determine catalytic activity for the HER. By designing new catalyst materials for the HER, we have expanded our understanding of the surface structures and properties that govern HER activity and stability. By applying this knowledge towards next generation catalyst design, we have developed several earth-abundant HER catalysts, including carbide-, nitride- and phosphide-based materials, with activities approaching that observed for platinum.
CO2 Reduction Reaction
Electrochemical reduction of CO2 has a potential of becoming a major contributor to sustainable production of fuels and chemicals through the use of renewable CO2 free energy sources. However, the development of an effective catalyst is vital, as there are currently no industrial scale operations that utilize this technology due to the low energetic efficiency. In our group, we focus on gaining fundamental understanding of the surface chemistry by tuning some of the key catalyst characteristics, such as the composition, the surface structure, and the morphology, as well as other factors, such as electrolyte composition and reaction conditions. By implementing the insights gained from our work, we aim to design effective catalysts that would allow for the industrialization of the technology.
Oxygen Evolution Reaction
The oxygen evolution reaction (OER, 2H2O → O2 + 4H+ + 4e-) is the complementary anodic half reaction in electrochemical water splitting. Requiring four proton and electron transfers per oxygen molecule, the OER is the more complex of the two half reactions and is consequently responsible for the majority of inefficiency in electrolyzer devices. In acidic media, only Ir-based catalysts have shown high activity and stability for the OER. To reduce dependence on expensive and rare precious metal catalysts, we aim to develop higher performance, low Ir-content materials for the OER . In alkaline media, catalyst material restrictions are relaxed and many first-row transition metal oxides show high activity for the OER. We aim to developed high performance OER catalysts , determine to origin of enhanced activity through advanced characterization techniques , and incorporate high performance catalysts into devices . The EERL seeks to develop novel, high performance OER catalysts through fundamental understanding of the structure-function relation of the catalyst surface to enhance efficiency and promote increased commercialization of energy storage devices.
Oxygen Reduction Reaction
Research Highlights
The oxygen reduction reaction (ORR) is a pertinent process in many electrochemical energy conversion and storage technologies, including fuel cells and rechargeable metal-air batteries. In acidic conditions, only platinum-based catalysts have shown sufficient activity and durability for practical purposes, although comes at a high cost and relies on limited global platinum supplies. Research in our laboratory focuses on designing improved activity ORR catalysts, with significantly reduced or eliminated platinum contents. Some strategies that have been employed to achieve this include the use of solid solution or intermetallic platinum alloys, shape controlled nanostructures to achieve preferential facet exposure, or the preparation of core-shell nanoparticles that can tune the interactions (i.e., binding energies) with ORR intermediate species. Our aim is to develop an improved understanding of the ORR process occurring on various surfaces, providing fundamental insight that can rationally guide our design of new catalyst materials.
In alkaline conditions, the ORR is a much more facile process and provides opportunity for non-platinum catalyst alternatives, including metal oxides, nanostructured carbons and silver-based catalysts. The ORR process on these surfaces is poorly understood in comparison to platinum, and the activity still lags behind that of platinum on a turn over frequency basis. We aim to develop new material designs and develop a thorough understanding of the surface structures and properties that influence intermediate adsorption energies and ORR activity on various alkaline-based catalysts.
The ORR can also proceed by a 2 electron reduction mechanism, forming hydrogen peroxide species. While this is undesirable from an energy efficiency standpoint for fuel cells (only 2 electrons transferred per oxygen molecule to form hydrogen peroxide as opposed to 4 to form water), this electrochemical reaction is advantageous because it could replace the energy intensive anthraquinone process conventionally used to synthesize hydrogen peroxide. This electrochemical synthesis could, for example, be coupled to renewable sources of energy (i.e., wind or solar) to provide on site generation of hydrogen peroxide. As a powerful oxidizer, distributed production of hydrogen peroxide could play an important role for drinking water treatment or sterilization applications.
Energy Storage and Device
The global climate change crisis combines the impacts of excessive use of fossil fuels with anticipated severe socioeconomic and political consequences. Replacing carbon-based fossil fuels with clean energy harvested from renewable resources (solar, wind, tidal, geothermal and so on) is the only viable long-term solution to address climate change. Due to the intermittent nature of renewable energies, energy-storage solutions should be implemented alongside. Lithium-ion batteries (LIBs) are one of the most promising technologies. Rechargeable lithium-ion batteries based on manganese oxide electrode materials are more environmentally friendly than conventional ones but generally suffer from rapid performance fading. A recent study sheds light on possible remedies through engineering of the interface.
Rechargeable metal–gas batteries have the promise of exceeding the energy densities of Li-ion batteries. An typical metal–gas system is the non-aqueous lithium–oxygen (Li–O2) battery, which was developed with a view to deploying it in electric vehicles. However, operating this battery comes with substantial challenges that include parasitic chemical reactivity and degrees of electrochemical irreversibility, which contribute to poor charging and cycling. To address these challenges, researchers began exploring new non-aqueous metal–gas battery paradigms by manipulating the underlying O2 redox behaviour through electrolyte and materials design, using non-Li-metal anodes to change the nature of the solid discharge phase and improve reversibility, and using other gaseous reactants as the cathode. This Review presents the new understanding of non-aqueous gas-to-solid electrochemistry that has emerged from these concerted efforts, along with new hurdles that have been revealed as cells have gradually been reformulated. The ultimate impact of new metal–gas batteries needs to be re-examined for applications beyond electric vehicles that are more amenable to the individual chemistries.
Electrochemical reduction of CO2 has a potential of becoming a major contributor to sustainable production of fuels and chemicals through the use of renewable CO2 free energy sources. However, the development of an effective catalyst is vital, as there are currently no industrial scale operations that utilize this technology due to the low energetic efficiency. In our group, we focus on gaining fundamental understanding of the surface chemistry by tuning some of the key catalyst characteristics, such as the composition, the surface structure, and the morphology, as well as other factors, such as electrolyte composition and reaction conditions. By implementing the insights gained from our work, we aim to design effective catalysts that would allow for the industrialization of the technology.
