Electrical Energy Storage with Engineered Biological Systems

Abstract

The availability of renewable energy technologies is increasing dramatically across the globe thanks to their growing maturity. However, large scale electrical energy storage and retrieval will almost certainly be a required in order to raise the penetration of renewable sources into the grid. No present energy storage technology has the perfect combination of high power and energy density, low financial and environmental cost, lack of site restrictions, long cycle and calendar lifespan, easy materials availability, and fast response time. Engineered electroactive microbes could address many of the limitations of current energy storage technologies by enabling rewired carbon fixation, a process that spatially separates reactions that are normally carried out together in a photosynthetic cell and replaces the least efficient with non-biological equivalents. If successful, this could allow storage of renewable electricity through electrochemical or enzymatic fixation of carbon dioxide and subsequent storage as carbon-based energy storage molecules including hydrocarbon and non-volatile polymers at high efficiency. In this article we compile performance data on biological and non-biological component choices for rewired carbon fixation systems and identify pressing research and engineering challenges.

Constraints on the Efficiency of Engineered Electromicrobial Production

“…To date, these mediators include H 2 , [22][23][24][25] inorganic ions like ferrous ions, 26 ammonia, 27 and the simple organic molecule formate. 22,[28][29][30] Additionally, carbon monoxide, formaldehyde, methane, methanol, phosphite, and reduced sulfur compounds (H 2 S, S 2 O 2À 3 , S 4 O 2À 6 ) could also be used as redox mediators, 7 but we are unaware of any demonstrations to date. These electron shuttles can either be directly electrochemically reduced or produced by reaction of electrochemically reduced H 2 with CO 2 or another inorganic compound, or both.…”

“…While the number of electrons needed to produce a molecule of fuel is higher in a DET-mediated system than in an otherwise comparable H 2 -mediated system using the same CO 2 -fixation pathway, the whole-cell voltage in a DET-mediated system is lower than in a H 2 -mediated system (DU cell R1.23 V for H 2 but only R0.92 V for DET) as the redox potential of Mtr is much lower than H 2 . 113 Furthermore, the bias voltages at lab-scale remain approximately the same, 7 meaning more total current is available to a DET-mediated system. However, DET-mediated EMP is approximately twice as sensitive to changes in transmembrane voltage than a H 2 -mediated system (Figure S1).…”

“…[1][2][3] However, to enable high penetration of renewables onto the grid, energy storage with a capacity thousands of times greater than today's will be essential. [4][5][6][7] On top of this, despite significant advances in electrified transportation, the need for hydrocarbons in many applications such as aviation could persist and even grow for decades to come. 3 Likewise, the need to sequester tens of gigatonnes of CO 2 per year will also continue to grow.…”

“…8,9 Electromicrobial production (EMP) technologies that combine biological and electronic components have the potential to use renewable electricity to power the capture and sequestration of atmospheric CO 2 and convert it into high-density, non-volatile infrastructure-compatible transportation fuels or energy storage polymers. 7,[10][11][12][13][14] At least two big classes of EMP technologies exist. 13,15 Given the rapid evolution of the field, these definitions can vary from author to author and may soon change, 15 but at the time of writing we believe they represent a widely acceptable classification.…”

Understanding Electron Transfer Reactions using Constrained Density Functional Theory: Complications due to Surface Interactions

“…Electron transfer (ET) is a key process in all redox reactions in (bio-) chemistry, [1][2][3] from natural photosynthesis to cellular respiration to electricity storage and conversion technologies. [4][5][6][7][8][9][10][11] The importance of this area was highlighted by 1992 Nobel Prize in Chemistry awarded for Rudolph Marcus "for his contributions to the theory of electron transfer reactions in chemical systems". Understanding electron transfer reactions is also of crucial importance in selecting materials for flow batteries, a key candidate for stationary energy storage for storing wind and solar energy.…”