Bulk protonic conductivity in a cephalopod structural protein

Abstract

Proton-conducting materials play a central role in many renewable energy and bioelectronics technologies, including fuel cells, batteries and sensors. Thus, much research effort has been expended to develop improved proton-conducting materials, such as ceramic oxides, solid acids, polymers and metal-organic frameworks. Within this context, bulk proton conductors from naturally occurring proteins have received somewhat less attention than other materials, which is surprising given the potential modularity, tunability and processability of protein-based materials. Here, we report proton conductivity for thin films composed of reflectin, a cephalopod structural protein. Bulk reflectin has a proton conductivity of ~2.6 × 10(-3) S cm(-1) at 65 °C, a proton transport activation energy of ~0.2 eV and a proton mobility of ~7 × 10(-3) cm(2) V(-1) s(-1). These figures of merit are similar to those reported for state-of-the-art artificial proton conductors and make it possible to use reflectin in protein-based protonic transistors. Our findings may hold implications for the next generation of biocompatible proton-conducting materials and protonic devices.

Self-assembled two-dimensional nanofluidic proton channels with high thermal stability

“…To study the temperature effect on nanofluidic ionic current, a vermiculite membrane is embedded into a PDMS block along with a thermometer, and the PDMS block is heated in an oil bath, as shown schematically in Fig. 4a nanochannels by a Grotthuss mechanism [29][30][31] . In this mechanism, charge is transported by the coordinated hopping of protons between water molecules in the nanochannels.…”

Protonic transistors from thin reflectin films

“…We find that the majority of the device metrics, including mobility and proton concentration, are comparable to those previously reported for protonic transistors from reflectin films with a thickness between ∼1 and ∼2 µm. 21 However, we observe a 2-fold improvement in the thin protonic transistors' I HIGH /I LOW current ratios. Overall, our findings highlight the importance of the active layer geometry for the performance of protein-based (and other) protonic transistors.…”

“…21 This finding enabled the fabrication of protein-based protonic transistors with excellent figures of merit, including a proton mobility (µ H+ ) of ∼7.3 × 10 −3 cm 2 V −1 s −1 . 21 However, due to active layers with thicknesses between ∼1 and ∼2 µm, the transistors possessed relatively poor I HIGH /I LOW ratios of ∼1.6. Herein, we build upon our previous work and demonstrate improved I HIGH /I LOW current ratios for reflectin-based protonic transistors.…”

Long‐Range Proton Conduction across Free‐Standing Serum Albumin Mats

“…Several studies have followed proton conductivity across collagen,27 keratin,28 and lysozyme layers 29, 30. Recently, Gorodetsky and co‐workers31 showed that upon drop‐casting reflectin (a structural protein found in cephalopods) and drying it between two electrodes, they could measure a proton conductivity across the film of 0.1 mS cm −1 at room temperature, and up to 2.6 mS cm −1 at 65 °C.…”

“…In this mechanism the proton hops from one water molecule to another, and it is expected to have activation energy of 2–3kcal mol −1 (≈90–130 meV), and a KIE of 1.4 7. Gorodetsky and co‐workers31 and Rolandi and co‐workers23, 25 explained the high proton conductance of dry films of the relectin protein and polysaccharides, respectively, by the Grotthuss mechanism, and also suggested that the protein film contains water channels that support proton conductivity. In the work of Gorodetsky and co‐workers',31 similar KIE (≈1.7) values as expected for the Grotthuss mechanism have been found but with a slightly larger E a value (≈0.2eV) 31…”