Have you ever used data from an EEG-database or repository? Are there platforms or services for sharing electrophysiological data that you can recommend? What were your experiences using data repositories?
In the field of Brain Computer Interface (BCI), there is a long history of sharing EEG data.
I recommend this repository : http://bnci-horizon-2020.eu/database/data-sets
You can post your own dataset, as long as you have the consent of the subject and data are anonymized.
your data don't necessary need to be a pure BCI recording, to some extend, any EEG data recorded during different condition can be view as a BCI problem (decoding / classification of brain activity) and can found their place in this repository.
People use figshare to make research data publicly available (and obtain a persistent DOI for the data as well). An example is the MAMEM project (funded by the European Commission). They just made available a pretty unique dataset for work on brain computer interfaces.