My research specialty is design and synthesis of functional materials for energy-associated applications. Specifically, my research involves three main projects:
1. [Primary] Carbonaceous materials for supercapacitors Supercapacitors are charge storage devices capable of charging and discharging at much faster rates (in seconds) than conventional batteries (in hours). They are used in operations of lifts, emergency doors, back-up power stations and race cars, and in compliment to solar cells for electricity storage or lithium-ion batteries to power electric vehicles. Below are two videos showing laboratory-made supercapacitors that power a timer (upper) and a red light-emitting diode (bottom).
This project mainly deal with carbon-based materials:
Light-weight supporting substrates for pseudo-capacitors. My research focuses on the development of light-weight carbon-based substrates for pseudo-capacitors alternative to the conventional metal-based substrates. These substrates have improved the gravimetric energy and power densities of pseudo-capacitors. Representative research works include the 3D graphene scaffold serving as a light-weight scaffold for manganese dioxide [Nano Lett., 15, 3189-3194 (2015)], and block-copolymer-derived porous carbon fibers for compositing with manganese dioxide nanosheets [Nat. Commun., 10, 675 (2019)].
Active materials for charge storage. Carbon itself can store charges via formation of electrical double layers at electrode-electrolyte interfaces. Highly porous carbons with ultrahigh surface areas are desirable supercapacitor electrodes. My research focuses on the design and synthesis of hierarchical porous carbons as supercapcitor electrodes. Representative works include 3D-printed graphene aerogels [(Nano Lett., 16, 3448-3456 (2016)], chitosan-derived hierarchical porous carbon foams [Nano Res., 9, 2875-2888 (2016) and Nano Lett., 17, 3097-3104 (2017)], and block-copolymer-derived porous carbon fibers [Sci. Adv. 5, eaau6852 (2019)].
Collaborators: Prof. Yat Li (Professor in University of California, Santa Cruz) Dr. Marcus A. Worsley (Staff Scientist in Lawrence Livermore National Lab); Dr. Cheng Zhu (Staff Scientist in Lawrence Livermore National Lab); Prof. Xihong Lu (Associate Professor in Sun Yat-sen University, Guangdong, China); Dr. Teng Zhai (Assistant Professor in Nanjing University of Science and Technology, Nanjing, China); Prof. Xiaoxia Liu (Professor in Northeastern University, Shenyang, China); Prof. Feng Zhang (Associate Professor in Yancheng Institute of Technology, Yancheng, China)
2. Anode materials for microbial fuel cells Microbial fuel cells are a sub-family of fuel cells which employ bacteria to convert organic matters or pollutants to electrical energy, simultaneously yielding methane gas, hydrogen gas, or liquid fuels as byproducts. They are promising devices for water treatment and power generation, and have find applications in wastewater treatment plants and breweries. In collaboration with Dr. Yang Yang at Northwestern Polytechnical University, China, we explore and synthesize novel carbonaceous architectures as anodes for bacteria colonization. A representative work is the nitrogen-doped graphene aerogel which enabled large-density bacterial colonization and significantly advanced the power-generation capability of microbial fuel cells [Adv. Sci., 3, 1600097 (2016)]. Collaborator: Dr. Yang Yang (Assistant Professor, Northwestern Polytechnical University, China)
3. Semiconductors for solar-driven photo-electrochemical water splitting Water splitting with solar light and semiconductors is an environmentally benign and sustainable way to obtain hydrogen fuel, an emission-free energy source. Solar harvesting represents the very first step of solar water splitting. We aim at making semi-conductors to achieve state-of-the-art performance as well as addressing fundamental drawbacks of semiconductors, such as the poor electrical conductivity of hematite and the narrow light-absorption wavelength spectrum of titania. We recently discovered that the titanium dioxide, a transition metal oxide believed to be a stable photo-anode, experienced an apparent decay in photo-current after a prolonged working duration. We revealed that the instability was caused by photo-hole corrosion. Such instability can be alleviated through addition of hole scavengers, e.g., methanol, into electrolytes [Nano Lett., 15, 7051-7057 (2015)]. Collaborators: Prof. Xihong Lu (Associate Professor in Sun Yat-sen University, Guangzhou, China); Prof. Gongming Wang (Professor in University of Science and Technology, China, Hefei, China)
4. Heteroatom-Doped Carbon-based Materials as Efficient Catalysts This project actively explores hierarchically porous carbon materials doped with oxygen, nitrogen, sulfur atoms etc as well as uniquely porous structures for catalytic applications including: oxygen reduction reaction (ORR), carbon dioxide reduction (CO2RR), sulfur removal, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). One representative work is the hierarchially porous carbon foams derived by carbonizing chitosan, the second to the most abundant bio-polymers, in a gas atmosphere blending ammonia and nitrogen [ACS Appl. Energy Mater. 1, 5043-5053 (2018)].
Collaborators: Prof. Gongming Wang (Professor in University of Science and Technology, China, Hefei, China); Prof. Scott Oliver (Professor in University of California, Santa Cruz).