About

Thomas E. Mallouk is the Vagelos Professor in Energy Research and a Professor of Chemistry at the University of Pennsylvania. He holds a B.S. in Chemistry from Brown University obtained in 1977 and a Ph.D. in Chemistry from the University of California, Berkeley, completed in 1983. His research focuses on energy-related chemistry, contributing to the understanding and development of chemical processes relevant to energy applications. As a distinguished faculty member, he is involved in teaching and mentoring within the Department of Chemistry, and he holds the position of Department Chair and Graduate Chair, demonstrating his leadership role within the academic community.

Research topics

• Computer Science
• Materials science
• Nanotechnology
• Chemistry
• Physics
• Biochemical engineering
• Engineering
• Organic chemistry
• Condensed matter physics
• Environmental science
• Optoelectronics
• Biology
• Composite material
• Thermodynamics
• Process engineering
• Quantum mechanics
• Physical chemistry
• Inorganic chemistry
• Mathematics
• Chemical engineering
• Theoretical physics
• Combinatorics
• Ecology

Selected publications

• Silver Oxide Nanoparticles as Solid-State Hydroxide Ion Conductors for Watt-Scale Anion Exchange Membrane Fuel Cells

  ACS Energy Letters · 2026-01-28

  articleOpen accessSenior authorCorresponding

  Inorganic solid-state hydroxide ion conductors have emerged as stable platforms for high-temperature alkaline energy conversion technologies. Although several materials have shown promising ionic conductivity in model studies, their direct implementation in operating devices has remained largely unexplored. Here, we demonstrate that silver(I) oxide (Ag2O) nanoparticles can function as hydroxide ion conductors within anion exchange membrane fuel cells (AEMFCs). Syringe-filtered 1–6 nm Ag2O nanoparticles were integrated into Pt/C cathodes, establishing ionic conduction pathways across the cathode–membrane interface. The resulting ionomer-free membrane electrode assembly (MEA) achieved 1.91 W cm–2 peak power density at 2.4 wt % Ag2O loading and maintained stable mass transport during 100 h of continuous operation at 0.6 A cm–2. Electrochemical and structural analyses revealed how Ag2O loading influences ionic conduction, pore structure, and mass transport behavior in ways that are partially distinct from conventional ionomer-based electrodes. These findings highlight inorganic solid-state conductors as promising design analogues to ionomers for high-performance, ionomer-free AEMFC cathodes.

  PublisherOA PDFDOI

• Electron Transfer Energetics in Photoelectrochemical CO2 Reduction at Viologen Redox Polymer-Modified p-Si Electrodes.

  UNC Libraries · 2026-03-07

  articleOpen access1st authorCorresponding

  While redox polymer-mediated catalysis at silicon photoelectrodes has been studied since the 1980s, there have been few detailed studies of these materials in photoelectrochemical CO₂ reduction. Here, we develop silicon photoelectrodes functionalized with a viologen-based polymer that mediates the formation of catalytic gold nanoparticles. The presence of gold was confirmed by X-ray photoelectron spectroscopy (XPS), and the nanoparticles were imaged with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We probed the CO₂ reduction process during bulk photoelectrolysis to find modest, yet consistent CO faradaic efficiencies across a range of applied potentials. Operando surface-enhanced Raman spectroscopy (SERS) was used to measure the Fermi levels of both the viologen polymer and the Au catalyst sites. The operando measurement of the Fermi levels of all three components of the photocathode provides a unified picture of the electron transfer process in the semiconductor-redox polymer-catalyst system. The redox polymer serves as the electron transfer mediator between the Si substrate and Au sites. In addition, the Au Fermi level equilibrates with the Fermi level of the viologen polymer, which in turn fixes the quasi-Fermi level of Au catalysts at the p-Si/redox polymer interface. This suggests a potential future direction of using redox polymers with tunable potentials to modulate the potential of metal cocatalysts and thus control the reaction selectivity.

  PublisherDOI

• A Monolithic Artificial Leaf for Solar Methanol Production from CO ₂ and H ₂ O

  Journal of the American Chemical Society · 2026-04-30 · 2 citations

  article

  . We further integrate the photocathode with a multijunction perovskite photovoltaic minimodule to afford a standalone solar fuel system, which demonstrates a light-to-methanol conversion efficiency of 0.8%, 32 times higher than the present record in light-to-alcohol conversion with an artificial leaf.

  PublisherDOI

• Charge Transfer Dynamics in Dye-Sensitized Photocatalysts Using Metal Complex Sensitizers with Long-Wavelength Visible Light Absorption Based on Singlet–Triplet Excitation

  ACS Catalysis · 2025-12-05

  articleOpen accessCorresponding

  An Os(II) polypyridyl complex was applied as a photosensitizer in dye-sensitized photocatalyst systems based on Pt-intercalated HCa2Nb3O10 and Pt-loaded TiO2. The Os(II) complex exhibits a spin-forbidden but partially allowed triplet metal-to-ligand charge transfer (3MLCT) transition, enabling broad visible light absorption up to 800 nm, which surpasses that of conventional Ru(II)-based dyes. Despite its shorter excited-state lifetime compared to Ru(II) complexes, efficient electron injection from the excited Os(II) dye into the semiconductor was confirmed. Under visible-light irradiation, the Os(II)-sensitized photocatalysts showed higher H2 evolution activity than the Ru(II)-sensitized photocatalysts when sodium ascorbate was used as an electron donor, demonstrating effective utilization of long-wavelength visible light. In contrast, negligible H2 evolution was observed when NaI was employed as a redox mediator for Z-scheme water splitting. Transient absorption spectroscopy revealed that the lack of activity stemmed from inefficient electron transfer from I– to oxidized Os(II). These findings highlight the importance of selecting appropriate redox mediators to fully exploit long-wavelength dyes for overall water splitting under visible light.

  PublisherDOI

• Automation of the Marangoni Effect for Making Well-Ordered and Transferable Colloidal Monolayers at the Air–Water Interface

  Langmuir · 2025-06-04 · 2 citations

  articleSenior authorCorresponding

  The ability to efficiently create ordered colloidal monolayers on solid surfaces is critical for nanosphere lithography and related applications. We describe here a simple automated method for growing well-ordered 2D crystals of polystyrene spheres at an air-water interface and transferring them to silicon substrates on the wafer scale. The method exploits the Marangoni effect and is enhanced by surface treatment of both the basin for monolayer formation and the intended substrate for transfer. Quantitative image analysis of the sphere monolayers shows that the monolayer packing is improved by automation. Dual-droplet automation is shown to be useful for controlling 2D crystal growth and forming phase-separated monolayers from two different colloidal particle sizes.

  PublisherDOI

• Electron Transfer Energetics in Photoelectrochemical CO₂ Reduction at Viologen Redox Polymer-Modified p-Si Electrodes

  Journal of the American Chemical Society · 2025-03-06 · 7 citations

  articleSenior authorCorresponding

  While redox polymer-mediated catalysis at silicon photoelectrodes has been studied since the 1980s, there have been few detailed studies of these materials in photoelectrochemical CO2 reduction. Here, we develop silicon photoelectrodes functionalized with a viologen-based polymer that mediates the formation of catalytic gold nanoparticles. The presence of gold was confirmed by X-ray photoelectron spectroscopy (XPS), and the nanoparticles were imaged with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We probed the CO2 reduction process during bulk photoelectrolysis to find modest, yet consistent CO faradaic efficiencies across a range of applied potentials. Operando surface-enhanced Raman spectroscopy (SERS) was used to measure the Fermi levels of both the viologen polymer and the Au catalyst sites. The operando measurement of the Fermi levels of all three components of the photocathode provides a unified picture of the electron transfer process in the semiconductor-redox polymer–catalyst system. The redox polymer serves as the electron transfer mediator between the Si substrate and Au sites. In addition, the Au Fermi level equilibrates with the Fermi level of the viologen polymer, which in turn fixes the quasi-Fermi level of Au catalysts at the p-Si/redox polymer interface. This suggests a potential future direction of using redox polymers with tunable potentials to modulate the potential of metal cocatalysts and thus control the reaction selectivity.

  PublisherDOI

• Surfactant Templating for the Subnanometer Thickness Engineering of Free-Standing Nonlayered Nanosheets

  ACS Nano · 2025-11-04

  article

  The precise control of thickness at the subnanometer scale is essential for tuning the properties of two-dimensional (2D) nanosheets. However, the thickness control of free-standing nanosheets composed of nonlayered compounds remains a fundamental challenge. Here, we report a solid-state surfactant templating strategy for synthesizing free-standing amorphous siloxane nanosheets with subnanometer thickness precision. By tailoring the length of ethylene oxide chains of the surfactant, we reproducibly obtained nanosheets with precisely defined thicknesses of 0.9, 1.5, 2.0, and 2.5 nm, while also enabling the incorporation of organofunctional groups into their frameworks. The resulting nanosheets exhibit thickness uniformity and high colloidal stability, enabling the formation of densely packed large-area films suitable for the systematic investigation of the properties, such as band gaps and breakdown strengths. We found that amorphous silica nanosheets showed exceptionally low overpotentials for the water dissociation reaction with a clear thickness dependence despite amorphous silica being widely regarded as a poor catalyst.

  PublisherDOI

• Data from: Solid-state hydroxide ion conductivity in silver(I) oxide, Ag₂O

  DRYAD · 2025-12-30

  datasetOpen accessSenior author

  Silver(I) oxide, Ag2O, precipitated as microcrystals by combining aqueous silver(I) nitrate and KOH solutions, was found to be a solid-state hydroxide ion conductor with ionic conductivity on the order of 10–3 S/cm. The proton chemical shifts at 4.87 and −7.35 ppm measured by solid-state 1H NMR experiments are attributed to water molecules and in-lattice OH– coordinated to silver, respectively. The lack of spinning sidebands around the 4.87 ppm peak indicates rapid reorientation on the NMR time scale, suggesting that the water molecules are adsorbed to the surface of the Ag2O crystals. Pulsed field gradient measurements gave similar diffusion coefficients (2 × 10–7 cm2/s at 298 K) for all three proton environments, indicating chemical exchange between sites on the millisecond time scale. The activation energy for OH– diffusion measured by NMR (0.18 eV) was comparable to that obtained by conductivity measurements and density functional theory (DFT) electronic structure calculations. The calculated Pourbaix diagram of Ag2O is consistent with the slightly lower sample density observed in He pycnometry and thermogravimetric measurements. The dataset here contains the theoretical calculations of this study to support the experimental results, including electronic band structure calculation, geometry relaxation, NMR calculations, and ion-migration calculations.

  PublisherDOI

• Spatially Patterned Architectures to Modulate CO₂ Reduction Cascade Catalysis Kinetics

  ACS Catalysis · 2025-03-26 · 4 citations

  article

  Electrochemical CO2 reduction using renewable sources of electrical energy holds promise for converting CO2 into fuels and chemicals. The complex interactions among chemical/electrochemical reactions and mass transport make it difficult to analyze the effect of an individual process on electrode performance based only on experimental methods. Here, we developed a generalized steady-state simulation to describe an electrode surface in which sequential cascade catalysts are patterned in a periodic trench design. If appropriately constructed, this trench geometry is hypothesized to be able to yield a higher net current density for a CO2 reduction (CO2R) cascade reaction. We have used realistic experimental reaction kinetics to investigate the role of trench geometry in mass transport, local microenvironments, and selectivity for a model CO2R cascade reaction. The model considers local concentration gradients of bicarbonate species at quasi-equilibrium and catalytic surface reactions based on concentration-dependent Butler–Volmer kinetics. Our results suggest that varying the spatial distribution of active sites plays a significant role in facilitating effective mass transport between active sites, modulating selectivity for the cascade reaction, and enhancing the yield of desirable cascade products. Moreover, we observe that this trench geometry significantly alters the cascade reaction rate by affecting the local pH, which can cause inadvertent depletion of available aqueous CO2 to limit the CO2R cascade kinetics and modest suppression of the hydrogen evolution reaction (HER). The results highlight the trade-offs between mass transport, pH, and reaction kinetics that become apparent only when considering the coupled physics of all processes at the electrode surface. This model can thus serve as a primary tool to build more selective and efficient patterned architectures for the CO2R cascade catalysis.

  PublisherDOI

• Correction to “Solid-State Hydroxide Ion Conductivity in Silver(I) Oxide, Ag₂O”

  Chemistry of Materials · 2025-01-10

  articleSenior author
  PublisherDOI

Recent grants

• Lamellar Inorganic Solids as Building Blocks for Functional Materials

  NSF · $531k · 2009–2013

• Layered Inorganic Solids as Building Blocks for Functional Materials

  NSF · $432k · 2013–2017

• NIH Grant R01GM043844

  NIH · $1.1M · 2000

• Assembly of Lamellar Materials from Nanoscale and Molecular Building Blocks

  NSF · $770k · 2001–2007

• Lamellar Inorganic Solids as Building Blocks for Functional Materials

  NSF · $524k · 2006–2010

Frequent coauthors

• Ayusman Sen

  47 shared

• W. Justin Youngblood

  45 shared

• Yoji Kobayashi

  King Abdullah University of Science and Technology

  44 shared

• Theresa S. Mayer

  Purdue University West Lafayette

  38 shared

• Pengtao Xu

  Shanghai Jiao Tong University

  37 shared

• Wei Wang

  34 shared

• Allen J. Bard

  The University of Texas at Austin

  33 shared

• Devens Gust

  Arizona State University

  32 shared

Labs

• Mallouk LabPI

  Not provided

Education

• B.S., Chemistry

  University of Pennsylvania

  1985

• M.S., Chemistry

  University of Pennsylvania

  1987

• Ph.D., Chemistry

  University of Pennsylvania

  1991