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This paper focuses on the in-depth analysis of the physical mechanism of the broadband frequency domain spectroscopy of oil-paper insulation. The complex permittivity shows two low-frequency dispersion phenomena, and the real part of the complex conductivity exhibits two slope changes under the synergistic effect of aging and moisture. The two slope changes are mainly attributed to the migration characteristics of water molecules and polar aging products with a degradation of the oil-paper insulation, resulting in the transition of the frequency dependence between the DC conductivity and AC conductivity. When the oil-paper insulation deteriorates seriously, the imaginary part of the dielectric modulus shows double relaxation peaks. Physical models of parasitic capacitance and molecular polarity interface polarization are proposed to reveal the physical mechanism of the double relaxation peaks. The left peak of the double relaxation peaks is caused by the accumulation of water molecules and polar aging products at the electrode/insulation interface, and the right peak is due to the charge disturbance of the cellulose molecular chain surface. This paper can provide theoretical support and technical guidance for the condition diagnosis and evaluation of oil-paper insulation.

In this work, the extended Debye model or Fourier transform is adopted to convert the polarization and depolarization current test results from the time domain into the frequency domain at low frequencies, thereby shortening the test time but producing large errors when the oil-paper insulation exhibits nonlinear characteristics. The voltage-current response characteristics of samples with three different moisture contents are tested to study the influence of moisture on the nonlinear characteristics. Hammerstein-Wiener (H-W) equivalent mathematical model is proposed for time-frequency domain conversion, and the results from this model and two formal methods are compared. The findings show that the errors of the two conventional methods increase with nonlinearity. The H-W model accurately depicts the nonlinear dielectric response of oil-paper insulation and thus can provide high-precision time-frequency domain conversion data.

In bioelectronic medicine and electroceuticals, electronic devices that conduct electrons are used to monitor and control ion-based biochemical reactions in order to detect and treat medical conditions. Advancing these devices will require a thorough understanding of the electrochemical pathways that transduce electronic currents into the ionic currents that interact with the natural system. Here, we analyze the tranduction of electronic current into a protonic current (H+) using Pd/PdHx contacts and a model proton conductor, chitosan. Linear sweep voltammetry and electrochemical impedance spectroscopy data indicate that, for Pd, limited proton injection occurs at the interface aided by water oxidation. For PdHx, H desorption and electrochemical oxidation to H+ lead to sustainable proton injection and transfer to the chitosan protonic conductor. We have developed electroanalytical expressions and predictive digital simulations that match the experimental results. This work confirms that PdHx contacts integrated in DC devices, in parallel with electrochemical impedance spectroscopy, comprise a suitable means for measuring H+ currents and interrogating the proton conductivity in biomaterials.

Charge transfer at the interface between the active layer and the contact is essential in any device. Transfer of electronic charges across the contact/active layer interface with metal contacts is well-understood. To this end, noble metals, such as gold or platinum, are widely used. With these contacts, ionic currents (especially protonic) are often neglected because ions and protons do not transfer across the interface between the contact and the active layer. Palladium hydride contacts have emerged as good contacts to measure proton currents because of a reversible redox reaction at the interface and subsequent absorption/desorption of H into palladium, translating the proton flow reaching the interface into an electron flow at the outer circuit. Here, we demonstrate that gold and palladium contacts also collect proton currents, especially under high relative humidity conditions because of electrochemical reactions at the interface. A marked kinetic isotope effect, which is a signature of proton currents, is observed with gold and palladium contacts, indicating both bulk and contact processes involving proton transfer. These phenomena are attributed to electrochemical processes involving water splitting at the interface. In addition to promoting charge transfer at the interface, these interfacial electrochemical processes inject charge carriers into the active layer and hence can also modulate the bulk resistivity of the materials, as was found for the studied peptide fibril films. We conclude that proton currents may not be neglected a priori when performing electronic measurements on biological and bioinspired materials with gold and palladium contacts under high humidity conditions.

The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists since the late 1960s. For several decades, the hydrationdependent electrical properties of eumelanin have mainly been interpreted within the amorphous semiconductor model. Recent works undermined this paradigm. Here we study protonic and electronic charge carrier transport in hydrated eumelanin in thin film form. Thin films are ideal candidates for these studies since they are readily accessible to chemical and morphological characterization and potentially amenable to device applications. Current−voltage (I-V) measurements, transient current measurements with proton-transparent electrodes, and electrochemical impedance spectroscopy (EIS) measurements are reported and correlated with the results of the chemical characterization of the films, performed by X-ray photoelectron spectroscopy. We show that the electrical response of hydrated eumelanin films is dominated by ionic conduction (10−4−10−3 S cm−1), largely attributable to protons, and electrochemical processes. To propose an explanation for the electrical response of hydrated eumelanin films as observed by EIS and I-V, we considered the interplay of proton migration, redox processes, and electronic transport. These new insights improve the current understanding of the charge carrier transport properties of eumelanin opening the possibility to assess the potential of eumelanin for organic bioelectronic applications, e.g. protonic devices and implantable electrodes, and to advance the knowledge on the functions of eumelanin in biological systems.

The ability of bioelectronic devices to conduct protons and other ions opens up opportunities to interface with biology. In this research highlight, we report on our recent efforts in bioprotonic devices. These devices monitor and modulate a current of protons with an applied voltage. Voltage-controlled proton flow mimics semiconductor devices with complementary transistors or biological behaviors such as synaptic-like memories and enzyme logic.

Two-terminal protonic devices with PdHx proton conducting contacts and a Nafion channel achieve 25 ms spiking, short term depression, and low-energy memory switching.

The euphoria from drinking alcoholic beverages makes them popular worldwide. Abuse in alcohol (ethanol) consumption leads to dependence, behavioral problems, and fatal accidents1. In 2013, 10,076 people lost their lives in alcohol-related-driving accidents in the United States alone, accounting for nearly 31% of all traffic related deaths1. Driving under the influence is illegal and the maximum allowed blood alcohol concentration (BAC) is 0.05–0.08%, in most countries2. A breathalyzer measures the concentration of ethanol in the breath to estimate the BAC of an individual. The first generation of breathalyzers uses a liquid dye sensitive to ethanol exposure, potassium dichromate, and a photodetector3. Reliability of these detectors is a challenge and potassium dichromate is environmentally toxic3. A new generation of breathalyzers uses the ethanol in the breath to power a fuel cell whose output is proportional to the ethanol concentration4. These breathalyzers are connected directly to smart phones to test one’s alcohol level before attempting to drive. However, these breathalyzers are still impractical because they require constant recalibration4. To-date the most reliable BAC tests and the only one that is admissible in court is the blood test, which is difficult to administer on site or for preventative purposes. A breathalyzer as easy to use as an inexpensive and disposable glucose paper-strip sensor would greatly simplify BAC testing5. Organic electrochemical transistors (OECTs) are excellent candidates for disposable biosensors because they are inexpensive, they can be made on flexible substrates, and they can be printed on paper6,7. OECTs are typically made with poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) PEDOT:PSS. PEDOT:PSS is a p-type organic semiconductor with several applications in bioelectronics8,9. Coupled with enzymes in the electrolyte, PEDOT:PSS OECTs are able to detect micro molar glucose concentration in human blood and sweat10. OECTs sensors are amenable to screen-printing11 and inkjet printing12 for rapid and inexpensive manufacturing. Here, we demonstrate an early stage proof-of-concept OECT-breathalyzer on paper by integrating a PEDOT:PSS OECT with the enzyme alcohol dehydrogenase. This proof-of-concept OECT-breathalyzer may aid the development of a breathalyzer that is easy-to-use, inexpensive, easily calibrated, and can be coupled with a cell-phone or a smart watch for BAC self-testing to reduce alcohol related traffic accidents.

Proton conduction is essential in biological systems. Oxidative phosphorylation in mitochondria, proton pumping in bacteriorhodopsin, and uncoupling membrane potentials by the antibiotic Gramicidin are examples. In these systems, H+ hop along chains of hydrogen bonds between water molecules and hydrophilic residues – proton wires. These wires also support the transport of OH− as proton holes. Discriminating between H+ and OH− transport has been elusive. Here, H+ and OH− transport is achieved in polysaccharide- based proton wires and devices. A H+- OH− junction with rectifying behaviour and H+-type and OH−-type complementary field effect transistors are demonstrated. We describe these devices with a model that relates H+ and OH− to electron and hole transport in semiconductors. In turn, the model developed for these devices may provide additional insights into proton conduction in biological systems.

With the recent physical demonstration of memristive-based devices low-power two terminal devices with memory and learning functions have advanced electronics and neuromorphic computing. To this end, typically slow moving ions are coupled with fast moving electrons. Ionic motion affords memory, with electronic current as the output signal. Here, we introduce fully ionic two-terminal devices in which protons provide both memory and output signal. These devices exhibit synaptic-like reversible short-term depression, memory, and can be turned “ON” and “OFF” with as little as 30 fJ of energy per bit if appropriately miniaturized.

In nature, electrical signalling occurs with ions and protons, rather than electrons. Artificial devices that can control and monitor ionic and protonic currents are thus an ideal means for interfacing with biological systems. Here we report the first demonstration of a biopolymer protonic field-effect transistor with proton-transparent PdH(x) contacts. In maleic-chitosan nanofibres, the flow of protonic current is turned on or off by an electrostatic potential applied to a gate electrode. The protons move along the hydrated maleic-chitosan hydrogen-bond network with a mobility of ~4.9×10(-3) cm(2) V(-1) s(-1). This study introduces a new class of biocompatible solid-state devices, which can control and monitor the flow of protonic current. This represents a step towards bionanoprotonics.

Translating ionic currents into measureable electronic signals is essential for the integration of bioelectronic devices with biological systems. We demonstrate the use of a Pd/PdHx electrode as a bioprotonic transducer that connects H+ currents in solution into an electronic signal. This transducer exploits the reversible formation of PdHx in solution according to PdH↔Pd + H+ + e−, and the dependence of this formation on solution pH and applied potential. We integrate the protonic transducer with glucose dehydrogenase as an enzymatic and gate for glucose and NAD+. PdHx formation and associated electronic current monitors the output drop in pH, thus transducing a biological function into a measurable electronic output.