Earth-Abundant Metal Catalysis for Sustainable Energy

Two-dimensional boron-based materials, including boride layers and borophene, are of growing interest due to their unusual electronic structures and potential applications in catalysis and energy storage. Although large-scale boron films can be synthesized on Cu(111), their precise structure remains debated, and distinguishing copper boride from borophene or mixed phases is still challenging. Chemical instability, especially the rapid oxidation of borophene in air, further limits practical use. In this work, we investigate two-dimensional copper boride grown on Cu(111) by diffusion-mediated synthesis. Surface analysis confirms the formation of copper boride, which resists oxidation by molecular oxygen, is reduced by atomic hydrogen, and undergoes reversible redox cycling between molecular oxygen and carbon monoxide, which are gases commonly present in catalytic environments. We find that molecular hydrogen does not reduce copper boride, indicating stability toward simple hydrogen exposure. In contrast, atomic hydrogen readily oxidizes the material at room temperature, although the boride tolerates partial oxidation without complete degradation. Oxidized copper boride can be reversibly reduced by carbon monoxide, demonstrating its ability to participate in catalytically relevant redox processes. These results establish the stability and redox behavior of two-dimensional copper boride and define the environmental conditions under which it remains functional, supporting its potential use in low-oxygen catalytic applications.

A solvent-free mechanochemical (ball-milling) method was employed to synthesize highly efficient bimetallic Cu2Ni1 catalysts supported on Al2O3 and ZnO for methanol steam reforming (MSR) studies. Comprehensive structural and surface analyses (XRD, TEM, BET, H2-TPR, XPS) revealed that this approach reduces crystallite sizes by as much as 83%, induces intimate Cu-Ni atomic mixing, and strengthens metal-support interactions, enabling the formation of highly reducible Cu-Ni solid solutions with a nanoscale domain size of 5-15nm. Among the catalysts, the Al2O3-supported catalyst (Cu2Ni1/Al2O3) exhibited the most superior structural and catalytic properties. Its strong Cu-Ni-Al interfacial bonding evidenced by high-temperature reduction features in H2-TPR and the smallest crystallite size provided exceptional anti-sintering stability, maintaining ≥ 90% methanol conversion and approximately 99% H2 selectivity over 60 hours of continuous reaction at 250 C. This stability mitigated deactivation pathways and restricted the formation of CH4 (methane). Conversely, the ZnO-supported catalyst (Cu2Ni1/ZnO) acted as an excellent promoter for low-temperature reducibility, yielding superior CO2 selectivity of ~97% at 150 C, but showed undesirable methanation at temperatures above 300 C. The observed performance is governed by a bifunctional mechanism where Cu sites drive methanol dehydrogenation, Ni sites activate water for the Water-Gas Shift (WGS) reaction, and the Cu-Ni interface synergistically enhances intermediate oxidation. This work validates mechanochemical synthesis as a facile and green pathway for engineering robust, high-performance Cu-Ni alloy catalysts for sustainable H2 generation.

Electrolyzers have been refined to reach a minimized gap between the electrodes, exemplified by the “zero gap” membrane electrode assembly in water electrolyzers. In this talk I will discuss the design and development of the Porous Solid Electrolyte (PSE) reactor, where this gap is re-opened to fully leverage ionic transport for broader applications beyond molecular transformations in electrolysis.

Carbohydrates represent the most abundant class of organic molecules in the biosphere, playing vital roles in numerous biological processes and serving as biofuels. Despite their significance, the study of metalloenzymes involved in carbohydrate metabolism, such as Xylose/Glucose isomerase (XGI), using synthetic models remains relatively underexplored. This presentation focuses on the synthesis of novel bi- and tetranuclear copper(II) and iron(III) complexes derived from a highly versatile, carboxylic-rich, heptadentate ligand, N,N’-Bis[2-carboxybenzomethyl]-N,N’-Bis[carboxymethyl]-1,3-diaminopropan-2-ol (H₅ccdp). This research is part of our investigation into the interactions between these complexes and biologically significant monosaccharides, which have important implications for various biological systems and renewable energy technologies. We have fully characterized the complexes K₄[Fe₄(ccdp)₂(o-phth)₂(OH)₂] and Na₃[Cu₂(ccdp)(µ-CO₃)]5H₂O using single crystal X-ray and spectroscopic techniques. Additionally, we have explored the interactions of these complexes with glucose, xylose, mannose, and xylitol in aqueous solution under varying pH conditions through spectroscopic methods. The characterizations, modes of sugar binding, and the apparent binding constants calculated for each monosaccharide with each complex will be discussed.

Secondary bonding interactions (SBI) such as hydrogen-bonding are widely recognized as critical components of many catalytic active sights. This is especially true in transformations that require coordination of multiple substrate binding events. Chalcogen-bonding (ChB) is a type of SBI that is mediated by heavier Group 16 elements. Despite its recognized utility in molecular recognition and analyte sensing, ChB has only just begun to be exploited in catalysis. The ability to integrate ChB in catalyst design is an intriguing strategy as the formation and dissociation of chalcogen-bonds is often a low-barrier process. Moreover, the nature of ChB SBIs is well suited to the cooperative binding and bond forming steps necessary to reductively couple carbon dioxide. We have examined the incorporation of chalcogen-bonding units in the form of benzotellurazole and isochalcogenazole (E = Se, Te) moieties into NNN chelating frameworks. The synthesis of these ligands has been accomplished in a straightforward manner and their coordination chemistry examined with a variety of transition metals. Structural studies of the coordination complexes demonstrate the presence of intermolecular chalcogen-bonding in several instances thereby validating the ligand design concept. Preliminary findings have also demonstrated that cobalt complexes of the isochalcogenazole ligands are active for reductive functionalization catalysis. The reactivity of these complexes will be discussed in the context of leveraging ChB interactions for CO₂ reduction.

The rising demand for Ru- and Ir-based photocatalysts poses risks due to their high cost, limited availability, and environmental impact, motivating the search for earth-abundant alternatives. Cr(III) polypyridyl complexes are promising candidates to replace these chromophores for photooxidation reactions and energy transfer processes, with long-lived excited states that can be tuned over 7 orders of magnitude (ns to ms). However, their broad adoption is limited by an incomplete understanding of the excited state processes that govern this reactivity. This work characterizes the excited state processes in Cr(III) chromophores to identify key structure-function relationships that govern photocatalyst performance.
Steady-state and time-resolved spectroscopy are used to quantify key photophysical properties of these metal-centered emitters, including the excited state lifetime and photoluminescence quantum yield. We demonstrate how simple synthetic perturbations using commercially available ligands can produce earth-abundant chromophores that outperform Ru(II) chromophores in singlet oxygen generation and [4+2] cycloaddition reactions. This work provides design principles for earth-abundant chromophores to reduce our reliance on precious metals, while performing desired organic reactions under mild conditions.

We have had a long-standing interest in designing new catalysts for CO2 reduction using earth abundant first row metals. We have synthesized novel CNC pincer ligands using NHC and pyridine donor groups for coordination to Co(I) and Ni(II) metal centers. The Ni(II) complexes are noteworthy for self-sensitized CO2 reduction to produce formate and CO. A record setting and long-lived metal centered excited state (ACS Catalysis, 2024) was believed to contribute to the promising catalytic properties. Further directions are being explored including the use of Co(I) complexes for CO2 hydrogenation reactions. An ultimate goal of this work is the formation of methanol and other high value products from CO2 hydrogenation or reduction. Several synthetic modifications to the metal complexes have been studied including 1) affixing electron donor or withdrawing groups to the pincer and 2) modification of the wingtip groups.