Renewable Energy Conversion: Organic Redox Flow Batteries and Electrocatalytic Carbon Dioxide Reduction
Creators: name: DeBruler, Camden R.
Publisher: name: Utah State University
Year: 2021

description: Steadily increasing global energy demands have pushed the industry to investigate renewable energy sources like solar and wind to help alleviate the strain on fossil fuel based non-renewable energy sources while also reducing carbon emissions. However, the energy producing power of these renewable technologies is limited by factors such as weather and the day-night cycle. Additional energy storage technologies are needed which are capable of storing excess energy during periods of high productivity, and delivering it when production rates fluctuate.
Batteries represent one possible energy storage device to meet this need. Specifically, redox flow batteries (RFBs) offer advantages in terms of easy scalability and inherent safety features which make them more attractive for large-scale installations compared to conventional lithium ion systems. RFBs traditionally use metals like vanadium to store energy, but this limited resource is not cost-effective in the long term. Recent research using all organic energy storage materials shows a better outlook for lowering the cost of the RFB system.
Here is reported several recent advances in organic materials for RFBs. Functionalized viologen molecules were shown to be very capable anode materials. Adding additional positive charges to the viologen structure doubled the available capacity of the cell, and increased the cell voltage up to 1.72 V. This is the highest reported cell voltage for an RFB using only organic active materials in a water based electrolyte. Adding additional negative charges to the viologen structure changed the overall charge of the molecule, giving this material compatibility with cathode materials previously unavailable for viologen systems. This research effectively broadened the versatility of viologen materials in water based redox flow batteries.
Also, the traditional RFB cell was modified to allow for simultaneous energy storage and seawater desalination. This device was capable of producing fresh water at an energy cost comparable to reverse osmosis systems while also storing energy. This device showed the potential to address both problems of water scarcity and renewable energy storage in one hardware installation.
Rather than store renewable energy in the form of electricity in batteries, it is also attractive to store it chemically in the form of chemical bonds. One possibility is to use renewable electricity to drive the conversion of atmospheric carbon dioxide (CO2) to fuels like methanol (CH3OH) or methane (CH4). This process is overall carbon neutral and can use atmospheric CO2 as a feedstock to help offset the emissions from traditional fuel combustion. This process requires a catalyst to increase the overall energy efficiency.
Here is reported a nickel catalyst system engineered to use electricity to drive the reduction of CO2 to usable fuels. The electronic characteristics and geometry of the catalyst were optimized for this reaction. The nickel catalyst showed the first reported evidence of a homogeneous catalyst converting CO2 to CH4, however, the result has not yet been confirmed in subsequent experiments.