Your question is too general. If you could be more specific, I could point out some good publications out there. But meanwhile, as you have mentionedmentioned Electrochemistry in your topic I can refer you to our papers published in EES (DOI: 10.1039/C1EE01039E) and AEM: (DOI: 10.1002/aenm.201200154). But one publication that I personally appreciate is this: http://www.pnas.org/content/early/2009/07/24/0905844106.full.pdf
But as an overall guideline, synergistic effects happen when the combination of different substances an produce an increased intensity in the property that you are measuring. it is well-known and documented in case of CNTs combined with other types of materials, such as graphene, graphene oxide, or polymers. The reason behind that can originate from the effective prevention of agglomeration or the bridging effects.