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THRUST M:   Catalyst Microenvironments

Molecular Tailoring of Catalysts and their Microenvironment for Durable and Selective Hybrid Photoelectrodes



Anna, Cahoon, Concepcion, Dempsey, Ertem, Fakhraai, Grills, Hammes-Schiffer, Hazari, Holland, Kanai, Lian, Lockett, Mallouk (co-Lead), Manbeck, Mayer (co-Lead), Meyer, Miller, Parsons, Polyansky, Stach, Tropsha, Wang 

The five-year goal of the Microenvironments Thrust is to learn how to purposely tailor the local environment around the catalyst on a molecular scale to direct reactivity along desired pathways for the reduction of CO2 and N2 to liquid fuels, and for the oxidation of water to O2

This Thrust aims to understand the micro-environment at semiconductor-catalyst interfaces and how to tailor it to alter activity, selectivity, and durability. LnM is a molecular catalyst and AG is an attachment group.

The local catalyst microenvironment forms at the semiconductor–catalyst interface in hybrid photoelectrodes. CHASE investigators will

  1. Create catalyst microenvironments containing various chemical functionality in hybrid photoelectrodes
  2. Systematically characterize these microenvironments
  3. Understand how the microenvironment influences activity, selectivity, and durability in liquid solar fuel production.

The conversion of sunlight, H2O, and CO2 and/or N2 to liquid fuels with hybrid photoelectrodes requires optimization of the catalyst, the light absorber, and the integration of these components (Integration Thrust). These assembled components under photoelectrochemical conditions create a catalyst microenvironment at the interface of the light absorber, the catalysts, and the solution. Such interfaces are where all of the processes of the liquid solar fuels challenge come together: photon-driven charge separation in the light absorber; efficient transfer of redox equivalents to a catalyst; and the many individual bond-forming and bond-cleavage steps using CO2, N2, acids, bases, and water. Thus, the catalyst microenvironment presents a wide range of opportunities for tuning activity, selectivity, and durability of the system. Nature provides compelling evidence that even seemingly simple changes in the catalyst environment can impart dramatic effects.

Optimizing hybrid photoelectrode performance will necessitate careful control over the microenvironment, which is currently poorly understood, difficult to interrogate, and hard to control. Overcoming these challenges requires progress on many new fundamental science challenges. The projects in the Microenvironments Thrust are motivated by specific hypotheses to address the following key research questions:

  • How can molecular surface modifications provide tailored microenvironments at semiconductor–catalyst interfaces to control the local electric field, proton activity, lipophilicity, and more?
  • How can spectroscopy and microscopy of hybrid surfaces provide insights into composition and structure of tailored microenvironments, and the chemical kinetics of catalysts in these microenvironments?
  • What microenvironments are best to enhance the desired synergistic interactions between the semiconductor light absorbers and molecular catalysts?
  • How can microenvironments be tailored to control photon-driven catalyst performance, including activity, selectivity, durability, resting state, and quantum efficiency?