Storing carbon as sodium formate has the same problem as storing it as trees - bacteria will eat it and release CO2. Its also not useful as portable fuel - its energy density is an order of magnitude less than kerosene.

Its potential use as a battery is interesting though. I can imagine a system where a long lasting catalyst is used to fill a tank of sodium formate using waste CO2 from industrial processes and excess electrical generation capacity from renewable sources like wind and solar, and the machines that use sodium formate to generate electricity at times of low wind and solar generation could potentially be less polluting overall compared to mining lithium for new batteries and recycling worn out lithium batteries.