Solar Fuels via Surface Molecular Catalysis

Department of Chemistry, University of New Hampshire

Nothing has such power to broaden the mind as the ability to investigate systematically and truly all that comes under thy observation in life -Marcus Aurelius

  Research

Project #1: Cooperative CO2 Reduction using Heterogenized Molecular Catalysts

In this project, we graft molecular catalysts onto solid-state surfaces to template intermolecular reactivity and enable cooperative activation of CO2 via low-energy pathways. We have successfully grafted a series of molecular catalysts on mesoporous SiO2 (Figure 1). The molecular catalysts include diimine-tricarbonyl Re(I) and Mn(I) complexes and macrocyclic Co(III) and Ni(II) compounds. Theoretical investigation of CO2 reduction on transition metal centers is being conducted in collaboration with Dr. Richard Johnson of UNH Chemistry.

                                          

Figure 1. Structures and pictures of different heterogenized molecular catalysts.

Project #2: Coupling Molecular Catalysts with Light-harvesting Surfaces for Solar CO2 Reduction

This project is focused on coupling molecular catalysts with energy sources, including semiconductor nanoparticles and nanostructured photoelectrodes. For example, we have deposited a macrocyclic Co(III) catalyst on TiO2 nanoparticles to achieve CO2-to-CO conversion upon UV irradiation (Figure 2a). In this project, we collaborate with Dr. Christine Caputo of UNH Chemistry and Dr. Tijana Rajh of Argonne National Lab to investigate photo-induced electron transfer and subsequent CO2-reduction catalysis. In another system, we utilize silicon nanowires as photoelectrodes to harvest light and transfer electrons to molecular catalysts for solar CO2 reduction (Figure 2b, in collaboration with Dr. Dunwei Wang of Boston College).

                                       

Figure 2. (a) Photocatalytic CO2 reduction on Co(III)/TiO2; (b) photoelectrochemical CO2 reduction on a silicon nanowire photoelectrode.

Project #3: Structure and Function of Interfacial Sites in Metal/TiO2 Photocatalysts

Photocatalysis on many TiO2 materials is relatively inefficient due to electron-hole recombination (dotted arrow, Figure 3a). This project uses earth-abundant metals to improve CO2 reduction on TiO2 photocatalysts. The transition metals, including Cu, act as electron sinks, promoting charge separation (Figure 3b). The goal of this project is to investigate the structure and function of interfacial sites in metal/TiO2 photocatalysts using spectroscopic techniques (Figure 3c). Theoretical studies are being conducted in collaboration with Dr. N. Aaron Deskins of Worcester Polytechnic Institute.

                                     

Figure 3. Charge separation in (a) TiO2 and (b) Cu/TiO2 photocatalysts. (c) FTIR spectra of CO adsorbed on Cu/TiO2. Abbreviations: CB (conduction band), VB (valence band), e- (electron), h+ (hole).

Project #4: Hybrid Photocatalysts for Organic Transformations

We are interested in carrying out organic transformations using hybrid photocatalysts based on earth-abundant elements. The hybrid photocatalysts are prepared by grafting transition metal catalysts onto surfaces. Currently we are investigating selective oxidation of different organic compounds on hybrid photocatalysts using molecular oxygen as the primary oxidant.

 

  Instrumentation

      Quantachrome NOVA 2200E BET Surface Area Analyzer                                 Cary 50 Bio UV-visible Spectrophotometer

 

Nicolet 6700 FTIR Spectrometer with in situ Transmission Probe    Nicolet 6700 FTIR Spectrometer with in situ Diffuse Reflectance Probe

                          Agilent 7820 Gas Chromatograph                                                               Electrochemistry Station

   

                  Varian Diffuse Reflectance UV-Vis Accessory                                        ThermoScientific Tube Furnace

                                                                      

                                               Hewlett Packard Ti-Series 1050 High Performance Liquid Chromatography