An Active 2D Molybdenum Carbide (MXene) Electrocatalyst
High-performance and low-cost electrocatalysts are needed to improve the kinetics of the hydrogen evolution reaction. We demonstrate for the first time, 2D Mo2CTx (MXene) as an active, non-precious metal electrocatalyst for hydrogen evolution, achieving a current density of 10 mA/cm2 at 189 mV overpotential without any special morphology design. Both theory and experiment indicate that the basal planes of Mo2CTx are catalytically active, unlike in the case of widely-studied MoS2. This paper is listed as a highly read paper on ACS Energy Letters.
A Highly Reversible Room-Temperature Sodium Metal Anode
Poor reversibility and undesirable dendritic growth of sodium metal anodes have plagued researchers for decades. Here, we discover a simple electrolyte combination: NaPF6 in glymes, that enables highly reversible and non-dendritic plating-stripping of sodium metal anodes, achieving an unprecedented level of Coulombic efficiency (99.9% over 300 cycles). Using this electrolyte, we demonstrate a stable room-temperature sodium-sulfur battery as well. This work was highlighted by ACS Central Science and featured as the journal's front cover.
In-Operando Optical Imaging of Lithium-Sulfur Batteries
Understanding the behavior of lithium-sulfur batteries in-operando (during real-time battery operation) is crucial in improving their performance. Here, we employ a custom-built electrochemical cell to study lithium-sulfur batteries using in-operando optical microscopy. Using this special cell design, we can directly visualize the temporal and spatial distribution of soluble polysulfide intermediates over the entire charge-discharge cycle, providing insight into degradation mechanisms and strategies to enhance the cycling stability of such batteries.
2D Layered Titanium Disulfide as Cathode Encapsulation Materials
For stable cycling performance, Li2S cathodes need to be well-encapsulated with materials that are both highly conductive and polar - something that is difficult to achieve in carbon-based materials. In this work, we demonstrate for the first time, the use of metallic and polar TiS2 to encapsulate Li2S cathodes, achieving fast charge-discharge (15 mins) and high areal capacity (3.0 mAh/cm2), the highest values ever reported for such cathode materials. This design concept can be generalized to other 2D layered transition metal disulfides such as VS2 and ZrS2 as well.
Battery Binders: A Combined Theoretical and Experimental Design
When it comes to improving battery performance, the role of binders that hold the electrode materials together is often neglected. In this work, we carried out rational materials design using high-throughput theoretical screening, which identified poly(vinylpyrrolidone) or PVP as a promising binder for Li2S cathodes. Experimentally, we achieved high cycling stability using PVP binder with ~70% capacity retention over 500 cycles. This paper was highlighted by US Department of Energy's SLAC National Accelerator Laboratory and Joint Center for Energy Storage Research.
Sulfur-Titanium Dioxide Yolk-Shell Nanoarchitecture
Next-generation lithium-sulfur batteries typically suffer from fast capacity decay and short cycle life. In this work, we designed a unique S-TiO2 yolk-shell nanostructure with specially-engineered internal void space. The result was a world-record lithium-sulfur battery with the lowest capacity decay (0.033% per cycle) and longest cycle life (1,000 cycles) ever reported. This work was highlighted by US Department of Energy's SLAC National Accelerator Laboratory and Joint Center for Energy Storage Research, as well as top journals including Science, Nature and Nano Energy.