438582 Rational Design of Electrochemical Interfaces for Control over Separation and Catalytic Processes

Sunday, November 8, 2015
Exhibit Hall 1 (Salt Palace Convention Center)
Xianwen Mao, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA

Although it is a well-established field in its own, electrochemistry has not yet been widely adopted as a control strategy for separation and catalytic processes, both of which are of central importance to chemical engineering. My research aims to establish design principles for efficient electrochemical interfaces, and develop novel electrochemical modulation strategies for separation and catalysis applications. An electrochemical interface generally consists of three key components: the electrode phase, the electrolyte phase, and the functional layer between these two phases. Rational design of an electrochemical interface for a specific application requires careful consideration of these three key constituents and the simultaneous electron/ion transport process across the interface. Identification of the critical factors that govern the efficiencies of electrochemical interfaces is also important for other future technologies of relevance to energy, the environment and health care.

First I will discuss several generalizable approaches to engineering the three key constituents for an efficient electrochemical interface: (i) electrode design with focus on tuning of electronic structure, together with theoretical calculations to elucidate the origin of anomalously high heterogeneous electron transfer (HET) kinetics obtained by modulating electronic properties of electrodes; (ii) molecular engineering of electrolytes with focus on synthesis of novel surfactant-like ionic liquids (SILs), combined with molecular dynamic (MD) simulations to decipher the unique structuring phenomenon of SILs in the bulk and near charged surfaces; (iii) surface functionalization of electrodes by redox-responsive materials with focus on improvement of accessibility of redox sites by creating nanostructured hybrid systems, and on elucidation of the charge transport mechanism in redox thin films.

Next I will discuss electrochemistry-based control strategies for several exemplary separation and catalytic processes, using highly efficient electrochemical interfaces with optimized structural, electronic, and chemical properties. First, I will show a new electrochemical mediation strategy for separation of organics-water mixtures using materials that exhibit redox-tunable hydrophobicity, and for separation of ion-ion mixtures using materials that bear stimuli-controlled charge densities. Second, I will introduce a catalysis control concept, electrochemically responsive heterogeneous catalysis (ERHC), that allows for temporal and spatial control of reaction kinetics and product selectivity in both batch and flow systems. In these examples, special attention is paid to (i) interrogating the relationship between electrochemical activities of material systems and the overall efficacies of separation or catalytic processes, (ii) comparing electrochemical modulation approaches to conventional methods in terms of energy consumption, and (iii) identifying general descriptors for high selectivity in separation and catalysis based on molecular-level interactions between target species and redox moieties.

With the new insights obtained into electrochemistry on electrode/functionalities/electrolyte systems, and the novel methodologies developed, my future research will expand on the concept of electrochemical modulation in order to achieve molecular precision in separation processes and synthetic chemistry, for environmental, energy and pharmaceutical applications. I will describe a few proposed projects consistent with this plan, such as (i) conductive networks with potential-dependent pore structures for highly selective one phase (liquid or gas) separation, (ii) biomimetic membranes with tunable multiphase transport properties using electrochemical gating mechanisms, and (iii) electrochemical control over radical-based chemical transformations to achieve high predictability and selectivity for synthesis of key pharmacophores. I expect that the materials and technologies that my group develops may be applied to a broad range of problems such as water treatment, protein separation, CO2 capture and transformation, environmental remediation, and drug discovery.

I aspire to introduce an unprecedented level of control in critical processes in chemical industries by developing new technology platforms based on “designer” electrochemical interfaces, elucidate the charge/electron transport mechanisms in complicated hybrid systems that are key to enhancing electrochemical activities, and advance the fundamental understanding of molecular-level interactions between target chemicals and the electrochemical interfaces using theoretical approaches. The long-term trajectory of my group will be defined by bringing the high precision, controllability, and energy efficiency of electrochemical modulation strategies to technologically important separation and catalytic processes at large scale.

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