a) Electrochemical reduction of CO2 to fuels and valuable chemicals

Electricity generated by renewable energy sources such as solar photovoltaics needs to be stored and transported. Besides using battery for energy storage, one promising technology is to use the electric power to convert CO2 into fuels and valuable chemicals (CO, methanol, ethylene, ethanol, etc.) in an electrochemical cell. In the area of eCO2RR, we develop cost-effective electrocatalysts to achieve high performance of CO2 reduction (Faradaic efficiency, product selectivity, low overpotential, etc.) The electroctalysts we developed include single atom metal (Fe or Ni) and nitrogen doped carbon (M-N-C) that demonstrates >95% CO selectivity at industrial viable current density (> 200 mA/cm2) in a flow cell, as well as Cu-based novel catalysts for multi-carbon production (>70% C2+ selectivity). An international patent is filed on scalable synthesis of heteroatom-doped carbon nanotubes (CNTs) as a low-cost catalyst for electrochemical CO2 conversion to CO. The materials synthesis utilizes commerically available materials as feedstock through a simple manufacturing process that can be scaled up to kilograms of catalysts per batch. The catalyst is now commercially available on Fuel Cell Store: heteroatom doped CNT-based catalyst for electrochemical reduction of CO2. In addition, copper (Cu) based electrocatalysts are under development with surface engineering approaches to achieve high selectivlty of muitl-carbon products like ethylene and ethanol from electrochemical CO2 reduction. For example, we developed ultrathin PTFE coated Cu nanoparticles that can achieve 78% Faradaic efficiency for C2+ products at a high current density of 400 mA/cm2.

b) Photocatalytic reduction of CO2 to fuels by sunlight

The goal of this research project is to effectively produce solar fuels by using CO2 and water as building blocks and novel TiO2 nanocomposites as photocatalysts. The climate change due to increased greenhouse gas concentrations in the atmosphere has revealed the urgent need to control CO2 emissions. Instead of sequestering the huge amount of CO2 in geological formations, using solar energy to recycle CO2 offers a brand new opportunity for simultaneous reduction of CO2 and production of energy-bearing compounds (e.g. syngas, methane, and methanol) that can be processed to liquid transporation fuels. We are developing nanostructured TiO2-based photocatalysts that can dramatically increase the efficiency of CO2 conversion to fuels by facilitating photoinduced charge transfer and improving utilization of the visible light. Recently, we have developed a hybrid adsorbant/photocatalyst material that can effectively adsorb and convert CO2 at a moderately-elevated temperature (150 C) with high catalytic stability, which is promising for power plant flue gas CO2 emission control.

c) CO2 reforming of methane by concentrated sunlight

CO2 and methane are two major greenhouse gases that may cause global warming, and they are also major components in natural gas and biogas. Conversion of CO2 and methane to produce syngas (CO and H2) presents an attractive way for sustainable energy production. In this project we apply concentrated solar to drive the reforming reaction and achieve synergistic photo-thermo-catalytic effects with high efficiency and stability.

a) Photocatalytic and electrocatalytic degradation of organic contaminants and disinfection in water

Advanced oxidation processes such as photocatalytic and electrocatalytic processes are an efficient way in degrading organic contaminants in water at a low cost. Sunlight can be used as the energy source to replace conventional UV lamps to achieve further energy saving. In this project, we develop a variety of nanostructured photocatalysts (TiO2 nanowires, Ag/TiO2 nanowires, TiO2/Fe2O3, BiOBr, etc.) and electrocatalysts (Sb-SnO2, FeCo2O4/CNT, etc.) to degrade various water pollutants (organic dyes, BPA, humic acid, etc.) and for disinfection of bateria and viruses under simulated solar irradiation.

b) Multifunctional nanofiber membranes with anti-fouling ability

This project focuses on fabricating and testing novel hybrid nanofiber materials and resultant membranes for concurrent filtration of fine particles and removal of multi-pollutants in water. Heavy metals (e.g., As, Cr) are removed through adsorption, while TOC (e.g., humic acid) and micro-contaminants (e.g. endocrine disruptors, pharmaceuticals) are decomposed upon photo-illumination. The hybrid materials have unique features of high surface area, high adsorption capacity, and ability of anti-fouling and on-site regeneration. They are advantageous over benchmark activated carbon adsorbents that are ineffective for heavy metal removal and suffer from capacity loss over regeneration cycles.

c) Membrane distillation and solar evaporation for clean water production

Membrane distillation (MD) is a thermally driven process in which phase change of wate from liquid to vapor occus on the membrane surface to separate water from contaminants and produce high quality distillate. An advantage of MD over other desalination techniques is that MD can utilize solar energy, geotehrmal energy, and industrial waste heat to heat up the solution thus reduce energy cost. It can also treat high TDS (total dissolved solids) water that is technically challenging. In this project, we assess the feasibility of using MD to treat oil/gas produced water by studying the effects of temperature, flow rate, and membrane fouling. We also apply solar energy to drive MD process.

Solar steam generation is an emerging technology of desalination by applying renewable solar energy. In this project, we developed a unique water desalination process by integrating solar steam generation with electrochemical degradation to treat saline water containing organics, and strong synergistic effects have been experimentally demonstrated.