Silicon dioxide based Electrochemical Metallization (ECM) cells were intensively studied as a promising candidate for CMOS compatible non-volatile memory devices. The resistance of ECM cells can be switched between a high resistive (OFF) state and a low resistive (ON) state by applying a sufficient voltage or current pulse. This resistance transition is attributed to the formation and rupture of a few nanometers in diameter metallic filament. However, the metal ion transport which is believed to be responsible for the filamentary switching mechanism is not understood in detail. In case of SiO2 we suppose protons or humidity may enhance the metal ion transport.

In this work we report our studies on the proton incorporation in amorphous SiO2 thin films focused on the impact of hydrogen and humidity on the resistive switching effect. The switching behavior was analyzed by current-voltage measurements performed at different ambient conditions. The incorporation of hydrogen has been confirmed by Time-of-Flight Secondary-Ion-Mass-Spectroscopy (ToF-SIMS). The results led to an expansion of the defect model proposed in the literature.

Impedance spectroscopy was applied on zeolite H-ZSM 5 as a proton conducting NH3 sensor material and DeNOx-SCR (selective catalytic reduction of NOx with NH3) catalysts at the same time under SCR conditions. We show that in situ monitoring of the NH3 conversion with NOx becomes feasible when the zeolite is loaded with NH3 first and NOx is applied afterwards to the gas phase. Temperature dependent measurements allow discriminating NH3 desorption from catalytic conversion and time dependent measurement give first hints on the thermal activation of the conversion.

Protons can fit into the perovskite structure because the O-O distance is approximately that of ice. However, to achieve charge balance, -2e charge must be added for every two protons added. If O2- vacancies are introduced, for instance by doping barium cerate with yttrium to obtain (BCY), each filled vacancy will add -2e charge. Proton concentration and conductivity can be increased by exposing BCY to steam molecules, which dissociate into 2 protons and an O2- ion. Our impedance spectroscopy measurements and solid oxide fuel cell (SOFC) work shows that exposure to H2 on the anode side can add protons. This requires addition of O2- ions on the cathode side from O2 in air. Alternatively, electrons could be added because BCY is a weak electronic semiconductor. BCY is a hole conductor, and this conductivity decreases upon exposure to steam or H2. From our analysis of V(i) curves for SOFCs with BCY electrolyte, at low H2 concentration, increasing this concentration decreases electronic conductivity somewhat, consistent with adding electrons and reducing hole carrier concentration. At higher H2 concentrations, electronic conductivity remains constant.

Proton transfer in perovskites such as BCY resembles that in usual H‑bonded crystals. Such transfer requires two steps, both needed for dc conductivity. One is intrabond proton transfer, O‑H O→O H-O. The other is a proton jump from one H-bond to an adjacent bond, equivalent to rotation of an O-H unit about the O ion. The main difference from usual H-bonded crystals is that the adjacent O-O pair most likely has no proton between the O ions, so that the Pauling ice rule precluding 2 protons in one bond is not much of a restriction in perovskites because the proton concentration is typically below 0.2 per formula unit. Another difference is that, though protonic semiconductor activation energies are high, in the 0.5 to 1 eV range, the high operating temperatures of SOFCs, 600 to 900 oC, give useful amounts of power per unit area, or in the electrolysis mode, useful amounts of H2 out for steam and electric power input.

Two applications for proton-conducting perovskite ceramics are SOFCs and hydrogen separation membranes (HSMs). For SOFCs, we have modeled the V(i) behavior with almost no adjustable parameters, and have succeeded in coming close to the Nernst open‑circuit potential as well as fitting the V(i) curves for a variety of H2/O2 partial pressure combinations. For HSMs, unlike for SOFCs, an electronic conductivity comparable to the protonic conductivity is desirable, to avoid using a cermet which may crack because of differential thermal expansion.

In conclusion, many oxides and fluorides have O-O or F-F separations in the H‑bonding range and will provide a stimulating playground for further basic and applied research on proton incorporation and dynamics in solids.

The configurations of proton channel network on the surface of Nafion® membranes were studied using current sensing atomic force microscopy after the membranes were annealed at elevated temperatures, aimed at understanding the effect of aging process in the membranes. The results reveal that proton conductance of the membranes becomes more uniform and the proton channels become chain-like aligning in parallel to the membrane surface. Accompanied to the configuration changes, the proton conductivity of the membrane shows an increase. As the annealing continues, the chain-like configuration for the proton channels persists but the conductance of the membranes decreases. The time constant of the conductivity decay decreases with increase of the annealing temperature. The observed changes can be attributed to reorientation of proton channels near the membrane surface from perpendicular to parallel to the surface as the annealing temperature approaches the glass transition of the membranes.

Micro-solid oxide fuel cells (Micro-SOFCs) with yttrium-doped barium zirconate (BZY) and strontium and cobalt-doped lanthanum scandate (LSScCo) electrolytes were fabricated for low-temperature operation at 300 °C. The micro-SOFC with a BZY electrolyte could operate at 300 °C with an open circuit voltage (OCV) of 1.08 V and a maximum power density of 2.8 mW/cm2. The micro-SOFC with a LSScCo electrolyte could operate at 370 °C; its OCV was about 0.8 V, and its maximum power density was 0.6 mW/cm2. Electrochemical impedance spectroscopy revealed that the electrolyte resistance in both the micro-SOFCs was lower than 0.1 Ωcm2, and almost all of the resistance was due to anode and cathode reactions. Although the obtained maximum power density was not sufficient for practical applications, improvement of electrodes will make these micro-SOFCs promising candidates for power sources of mobile electronic devices.

This paper presents results for the conductivity of BaCe0.85Y0.15O2-δ (BCY15) measured by electrochemical impedance spectroscopy in wet hydrogen and in Air, as well as test results from the application of the material in a new dual membrane fuel cell configuration (“IDEAL Cell”), in which the water is produced and evacuated through a separate chamber. The conductivity of dense BCY15 in wet hydrogen atmosphere at 700 °C is 2.0 10-2 S/cm. The measured values in air are of the same order. Preliminary tests of the material in the new cell design, where the three types of conductivity (protonic, oxide ion and mixed) are used in different cell compartments, are successfully performed.

In this work the release of atomic hydrogen from SiNx:H films is investigated. Thermal treatment as well as UV-illumination induces the formation of H2, increasing the tensile stress in the film. N-rich SiNx:H films release hydrogen only by UV-illumination, indicating involvement of charge trapping. Ab initio calculations show a possible reaction path for the release and diffusion of protons that also explain the diffusion of hydrogen into Si substrates.