NIMS and Hokkaido University jointly discovered that proton transfer in electrochemical reactions is governed by the quantum tunneling effect (QTE) under the specific conditions. In addition, they made a first ever observation of the transition between the quantum and classical regimes in electrochemical proton transfer by controlling potential. These results indicated the involvement of QTE in electrochemical proton transfer, a subject of a long-lasting debate, and may accelerate basic research leading to the development of highly efficient electrochemical energy conversion systems based on quantum mechanics.