Abstract
Energy production and storage is one of the foremost challenges of the 21st century. Rising energy demands coupled with increasing materials scarcity have motivated the search for new materials for energy technology development. Nanomaterials are an excellent class of materials to drive this innovation due to their emergent properties at the nanoscale. In recent years, two dimensional (2D) layered materials have shown promise in a variety of energy related applications due to van der Waals interlayer bonding, large surface area, and the ability to engineer material properties through heterostructure formation. Despite notable results, their development has largely followed a guess and check approach. To realize the full potential of 2D materials, more efforts must be made towards achieving a mechanistic understanding of the processes that make these 2D systems promising. In this perspective, we bring attention to a series of techniques used to probe fundamental energy related processes in 2D materials, focusing on electrochemical catalysis and energy storage. We highlight studies that have advanced development due to mechanistic insights they uncovered. In doing so, we hope to provide a pathway for advancing our mechanistic understanding of 2D energy materials for further research.
Highlights
Meeting growing energy demands is perhaps the greatest problem facing humanity in the 21st century
Liu et al used surface-sensitive soft x-rays to track the oxidation state in both LiCo1/3Ni1/3Mn1/3O2 and LiFePO4 electrode materials.[99]. While their operando x-ray absorption spectroscopy (XAS) of the Ni oxidation state correlated with the electrochemical cycling of the battery, they found that the oxidation state of Fe did not
scanning transmission x-ray microscopy (STXM)/XAS revealed the heterogeneous delithiation of the cathode via the formation of filament-like regions of FePO4 and demonstrated that the growth was governed by elastic effects rather than transport
Summary
Meeting growing energy demands is perhaps the greatest problem facing humanity in the 21st century. Heteroatom doped graphene has shown promising catalytic efficiency for oxygen evolution reactions (OER), oxygen reduction reactions (ORR), and HER.49,50 2D materials have been investigated as electrodes for intercalation-based energy storage devices. Intercalation, the reversible insertion of ions or molecules into the VDW gaps between the layers of 2D materials, is a widely used and promising technique to tune material properties, such as tuning the carrier density of the host material to induce superconductivity or to facilitate semiconducting to metallic phase changes.[44,51–53]. For developing MIBs beyond lithium-based batteries, 2D materials are attractive due to their mechanical flexibility, which can host larger ions than Li+, and a wide chemical compositional range, which can be tailored for specific intercalation processes. Promising classes of 2D materials as potential electrodes or electrode support materials for MIBs62–65 include TMDs,[23,25,27,30] MXenes,[16,29] and graphene or reduced-graphene oxide (rGO).19,22,24,26 2D materials have been explored as electrodes for intercalation-based supercapacitors.[16,66–69]
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