Palladium thin films for hydrogen sensing in aqueous electrolytes

Abstract

In this work, differently prepared palladium films are tested toward their hydrogen sensing properties in aqueous electrolytes. The Pd thin films were either electroless deposited, electrochemically deposited, or prepared by physical vapor deposition. The outcome of each fabrication process and characteristics of the Pd films were determined by means of SEM and cyclic voltammetry. Electrochemical impedance spectroscopy was performed in order to calibrate the prepared hydrogen sensors. The Pd films react on different hydrogen concentrations in the electrolyte by changing their electrical resistivity. Elemental hydrogen can diffuse into the Pd film leading to a lattice expansion and a phase transition. A second hydrogen sensing mechanism due to a change in charge transfer resistance can be observed.

Influence of atmospheric oxygen on hydrogen detection on Pd using Kelvin probe technique

“…Those samples have to be coated with palladium in order to enable hydrogen quantification based on the hydrogen concentration-dependent potential of Pd. Pd coatings can be realized by various methods like electrodeposition or physical vapour deposition (PVD) [31]. The deposition method determines the subsequent calibration routine as deposition methods can be divided into methods, which are characterized by a co-deposition of hydrogen and fabrication routes that ensure a hydrogen-free film.…”

“…Formation of the β-phase leads to change in several material properties such as decrease in electrical conductivity [28] and volume expansion of the Pd metal lattice [29]. On the one hand, this change in properties is the basis for hydrogen sensing [30][31][32], but on the other hand, it leads to drawbacks like hydrogen embrittlement [16,[33][34][35]. Based on the work of the Rohwerder group [36][37][38][39], Pd was introduced for sensing hydrogen in metals with Kelvin probe (KP) technique.…”

Indirect (hydrogen-driven) electrodeposition of porous silver onto a palladium membrane

“…There are other types of metal membranes that were studied for H 2 separation/ purification applications [19], although palladium offers an excellent choice since it provides (i) good ability to bind hydrogen, (ii) excellent H 2 permeability, and (iii) good catalytic surface properties. Additional tolerance to embrittlement due to H 2 (caused by an α-β phase transition for PdH x with x > 0.67 [20][21][22]) can be achieved, for example, by working with silver-palladium alloys [23].…”

“…Hydrogen gas as a reductant provides a further benefit as it is removed very easily without the need for further cleaning the product. In theory, hydrogen gas could be applied as a reducing agent for the production of many metals and materials [22]. Processes based on hydrogen permeation through palladium membranes are economically important [25,26].…”

Challenges in hydrogen quantification using Kelvin probe technique at different levels of relative humidity

“…In this case, also the production route of the investigated Pd surface makes a difference in the hydrogen uptake and diffusion behaviour. Pd thin films can be either electroless deposited, electrochemically deposited or prepared by physical vapour deposition, which shows varying performance for calibration of the hydrogen sensors by impedance spectroscopy [27]. The absorption of hydrogen by occupying vacancies causes several changes in the material.…”