Figure 1. Protonic device architecture and proton conductivity mechanism.

(a) Two and three terminal devices with PdHx source and drain. PdH_x is created by exposing Pd metal to 5% H₂ atmosphere. At this H₂ concentration, the Pd metal absorbs H₂ to form PdH_x with x ≈ 0.5. PdH_x is kept under 5% H₂ atmosphere throughout the measurements and acts as a H⁺ reservoir. The PdHx source and drain inject and sink protons into and from the proton wire according to the reversible reaction going from left to right at the source and from right to left at the drain. The PdH_x source and drain are connected to outside measurement electronics that measure the electronic current and complete the circuit. (b) Molecular structure of the H⁺-type proton conductor maleic chitosan, (c) Molecular structure of the OH⁻ -type proton conductor proline chitosan. Degree of substitution defined as q/n + m determines the doping level. (d) Hop and turn Grotthuss mechanism for conductivity of H⁺ as hydronium ion along a proton wire. (e) Equivalent mechanism for OH⁻ conductivity as proton hole along proton wire.