Penn State environmental engineering researchers discovered a way to utilize methanogenic archaea microbes to turn electricity directly to methane. The process is claimed to be 80% efficient and, if used to store wind and solar generated power for gas fueled power plants, could be carbon neutral if carbon dioxide exhaust is used to feed the microbes for further methane generation.
The chemical reaction from burning methane is pretty simple:
CH4 + 2(O2) →  2(H2O) + CO2 + heat
The electromethanogenesis reaction from archaea-coated biocathode electrodes reverses what happens when methane is burned:
2(H2O) + CO2 + electricity → CH4 + 2(O2)
A peer reviewed abstract dated last Wednesday is on the American Chemical Society site.