(Invited) Solving the Energy Storage and Energy Conversion Conundrum – Materials to the Rescue

Abstract

Energy storage systems have witnessed a meteoric rise ever since Sony commercialized the first Li-ion battery in 1994. Over the years, there have been a plethora of cathode, anode and electrolyte systems developed with stable cycle life and high coulombic efficiencies currently deployed in commercial electric vehicles. Similarly, alternate silicon and tin anodes were targeted as the next generation anodes to ubiquitous carbon. Recalcitrant volume expansion and ensuing solid electrolyte interphase (SEI) issues have reverted the focus back to the omnipresent high-energy density Li metal with efforts to overcome the ominous flammability and safety issues. Escalated impending demand for higher energy density have also made sulfur, an economic and common industrial effluent an attractive active material reverting attention back to Li-S batteries. Similarly, the portentous signs of global warming and the concomitant desire for developing green energy solutions have made hydrogen an imperative and attractive energy source providing the impetus for economic proton exchange membrane (PEM)-based water electrolysis (PEMWE) and fuel cells (PEMFCs). Like the energy storage field, PEMWE and PEMFCs have also witnessed intense research activity over the years following the early work on direct methanol fuel cells (DMFC). Developing high performance materials systems for energy storage and super responsive low-cost electrocatalysts still remain the major conundrum for developing high energy density and high-power density energy storage and conversion systems, respectively.This presentation will discuss the materials challenges that need to be overcome in Li-S batteries and PEM-based water electrolysis and fuel cells. Specifically, efforts aimed at achieving high-energy density cathodes and anodes as well as electrolyte additives for meeting the 500 Whkg-1 energy density targets for electric vehicle technology will be discussed. High sulfur (4-6 mg/cm2) loaded confined cathodes with unique ability to trap the pernicious polysulfide species combined with unique theoretical first principles calculations derived functional electrocatalysts exhibiting the propensity to reversibly catalyze the formation of Li2S and elemental S will be discussed. In tandem, progress made in generating new dendrite-free anodes and low-density current collectors exhibiting areal capacities as high as 15 mAh/cm2 with stable cycling over 100 cycles as well as electrolyte additives matching the cathode and anode performances will be outlined. Similarly, the journey into developing innovative low temperature chemical complexation approaches to novel bifunctional metallic nanostructured electrocatalysts first for DMFC systems and later how the unique approaches were modified targeting acid mediated PEMWE and PEMFCs comprising nanoscale metallic and complex ceramic doped oxide systems will be presented and discussed. Specifically, efforts made in the direction of realizing a unitized regeneration fuel cell (URFC) systems will be outlined and discussed in detail.