An electrochemical cell includes an anode including an anode catalyst, a cathode including a cathode catalyst, and a first set of proton-conducting metal nanoparticles between the anode and the cathode, such that the first set of proton-conducting metal nanoparticles is not in contact with the anode. The cathode may be a cathode assembly including a gas diffusion electrode, a cathode catalyst on the gas diffusion electrode, and proton-conducting metal nanoparticles on the cathode catalyst.