Dr. Bryan Hunter

Abstract:

The development of highly active earth-abundant catalysts for solar water splitting is critical for the innovation of noncarbon-based renewable fuels [1]. It is therefore important to determine the mechanisms of these water oxidation catalysts, such as nickel-iron layered double hydroxides ([NiFe]-LDHs), which exhibit low overpotentials, excellent long-term stability, and high current densities and Faradaic efficiencies [2]. In principle, mechanistic insight can pave the way for the development of new materials with enhanced activity.

We have developed a new, magnetic resonance-based technique to monitor the reaction kinetics of [NiFe]-LDH relative to other well-studied catalysts. This technique allows for nanomolar detection of oxygen isotopes and yields important information about the mechanism of these catalysts. Membrane inlet mass spectrometry and differential electrochemical mass spectrometry were instrumental in determining electrochemical properties in situ; however, they are indeed limited in their collection efficiency and quantification of oxygen on the minute timescale [4,5]. Results were paired with computational and kinetic modeling in order to differentiate key O–O bond-forming steps. Nickel-iron-based catalysts were shown to operate by a novel oxo-oxo coupling mechanism, distinct from hydroxide attack proposed for other systems—consistent with previous findings [3]. We present our initial findings and share our efforts at incorporating pulsed EPR experiments for these systems.