Nanoscale Imaging of Electrochemical Energy Conversion and Storage Systems

Justin Sambur, Colorado State University

Energy needs and environmental trends demand a large-scale transition to clean, renewable energy. Nanostructured materials are poised to play an important role in this transition. However, nanomaterials are chemically and structurally heterogeneous in size, shape, and surface structural features. Sambur's research group focuses on understanding the correlation between nanoparticle chemistry/structure and functional properties. The first part of his talk will focus on characterizing charge storage mechanisms in single nanoparticles. Sambur's lab has developed a high-throughput electro-optical imaging method to selectively probe the battery-like and capacitive-like (i.e., pseudocapacitive) contributions to overall charge stored in single metal oxide nanoparticles. Pseudocapacitors are a promising class of electrochemical energy storage materials that behave electrochemically like capacitors even though the underlying charge storage mechanism is faradaic in nature (like a battery). Pseudocapacitors have the potential to charge/discharge at capacitor-like rates and maintain high energy density. A major challenge in the field is to demonstrate that pseudocapacitors behave electrochemically like a capacitor and the charge storage process is faradaic in nature. It is challenging to do so because pseudocapacitive charging has the same electrical signatures as non-faradaic electrical double layer charging. Sambur will present his lab's recent single particle-level measurements that show (1) individual particles exhibit different charge storage mechanisms at the same applied potential and (2) particle size-dependent pseudocapacitive charge storage properties.

The second part of the talk will focus on solar energy conversion using ultrathin semiconductors such as monolayer-thick (ML) two-dimensional (2D) materials such as MoS2 and WS2. ML semiconductors represent the ultimate miniaturization limit for lightweight and flexible power generation applications. However, the underlying solar energy conversion processes in 2D materials is not entirely understood. Sambur's lab developed a correlated laser reflection and scanning photocurrent microscopy approach to study how layer thickness and surface structural features (edges versus basal planes) influence solar energy conversion efficiency. Sambur will highlight his recent wavelength-dependent photocurrent microscopy and current-voltage measurements that revealed charge separation, transport, and recombination pathways in monolayer heterojunction ITO/MoS2/WS2 and ITO/WS2/MoS2 photoelectrodes.