Bacteria batteries can store solar energy

RESEARCHERS have developed a microbial rechargeable battery (MRB), driven by bacteria, that can discharge stored solar energy over an eight-hour period.

The battery made by a team from the Netherlands’ Wageningen University (WU) and the research institute Wetsus operates in two stages. The first stage uses bacteria in a microbial electrosynthesis (MES) process to produce acetate in a CO₂ environment. The bacteria use excess energy from the solar panel to fix or reduce CO₂ into various molecules, one of which is acetate.

The second stage, a microbial fuel cell (MFC) involves the stored acetate broken down by exoelectrogenic, or electricity producing, bacteria, which are coated onto a bioanode. The bacteria consume the acetate. The biochemical process produces electrons, which are collected by the bioanode and then discharged when needed, like a battery.

The researchers say the MFC can operate on a 24-hour cycle, with 16 hours’ worth of solar energy required to charge the battery. The battery can be discharged for up to eight hours, mimicking the day-night pattern typical for solar energy production.

The next step for the team is to optimise its system, as the energy conversion efficiency is currently 40%, approximately half that of lithium-ion batteries. The team will also have to tackle the challenge of maintaining the current efficiency levels at higher power densities by developing a better counter electrode.

However, considering the manufacturing cost and safety concerns of large lithium batteries, the team believes the MRB will be more beneficial once these challenges have been overcome.

Sam Molenaar, agrotechnology and food sciences researcher at WU, spoke exclusively with The Chemical Engineer. He said, “When we broaden up the definition of efficiency to also include energy spent on the manufacturing, recycling/replacement of the battery, I think the MRB offers promising outlooks compared to ‘chemical’ alternatives.”

Environmental Science & Technology Letters, DOI: 10.1021/acs.estlett.6b00051