Well I would say why not go for the basic stuff. Formate ion is a week base right? and you are in a basic environment why not start to titrate your solution? first you will titrate the NaOH which is the strong base but then you might see also the peak(in the derivative) of your week base which will start to react after all the NaOH is consumed. You can use the potentiostat to measure the Potential as a function of time.

Another option is since formate can be oxidize to CO2 you can try to see if you get an oxidation wave using CV it will be something irreversible, and I am not sure how easy it will be to see it in a basc solution but you can give it a try.