Abstract:

As conventional oil and gas supplies are declining rapidly, relying solely on the current energy production methods is not an option. Developing innovative high-efficiency energy generation and high-density power storage technologies while reducing the environmental pollution are crucial to ensure a green and everlasting earth. Meanwhile, recent cutting edge process and characterization techniques developed in the field of nano provide unprecedented opportunities for forming and investigating novel materials that exhibit unusual physical and chemical properties unmatched by their conventional bulk counterparts. However, exploiting these nano-techniques to energy applications is still in its infancy. In my presentation, some reserach opportunities in this direction, especially those involve photovoltaic and electrochemical processes, will be discussed.

A photovoltaic processes involve the following steps: light absorbance, charge carrier generation, exciton diffusion, charge carrier separation and transport, as well as extraction/injection of carriers through contacts. In these multi-step processes, losses occur in thermalization, recombination, along with contact and junction voltage drop, which result in greatly reduced conversion efficiency. To achieve highly efficient light harvesting, the light-absorbing entities should be arranged in a special manner such that efficient photon absorption and minimal exciton self-quenching can be balanced. In addition, the distance between light-absorbing entities and the charge-separation sites should be comparable with the length scale for efficient energy transfer. Typical length scale is in the order of tens of nm. More over, the charge donor-acceptor separation should be short enough for the charge separation process to compete with relaxation to the ground state.

For energy generation by electrochemical and photo-electrochemical means, the key technology lies in how the fuels/water interact with the catalytic media. To maximize the probability of fuel-catalyst interaction, high-density nanometer-sized catalysts should be dispersed uniformly onto a good electron or proton conductors. The macro- and micro-structure of the hybrid catalyst-carrier support should be properly designed for effective mass/fuel transport. In addition, the catalyst must remain active for a substantial long period of time, which involves nanometer or even atomic-scale manipulation of catalysts and their support. Especially, tailoring the interface structure and surface bonding configurations so as to optimize the proton-electron generation and the subsequent energy/carrier transfer after catalytic reaction of the fuels is undoubtedly crucial for electrochemical energy cells.