Pawel Gazdzicki

Nanosized IrO(x)-Ir Catalyst with Relevant Activity for Anodes of Proton Exchange Membrane Electrolysis Produced by a Cost-Effective Procedure.

We have developed a highly active nanostructured iridium catalyst for anodes of proton exchange membrane (PEM) electrolysis. Clusters of nanosized crystallites are obtained by reducing surfactant-stabilized IrCl3 in water-free conditions. The catalyst shows a five-fold higher activity towards oxygen evolution reaction (OER) than commercial Ir-black. The improved kinetics of the catalyst are reflected in the high performance of the PEM electrolyzer (1 mg(Ir) cm(-2)), showing an unparalleled low overpotential and negligible degradation. Our results demonstrate that this enhancement cannot be only attributed to increased surface area, but rather to the ligand effect and low coordinate sites resulting in a high turnover frequency (TOF). The catalyst developed herein sets a benchmark and a strategy for the development of ultra-low loading catalyst layers for PEM electrolysis.

Oxygen adsorption on Pt/Ru(0001) layers

Chemical properties of epitaxially grown bimetallic layers may deviate substantially from the behavior of their constituents. Strain in conjunction with electronic effects due to the nearby interface represent the dominant contribution to this modification. One of the simplest surface processes to characterize reactivity of these substrates is the dissociative adsorption of an incoming homo-nuclear diatomic molecule. In this study, the adsorption of O(2) on various epitaxially grown Pt films on Ru(0001) has been investigated using infrared absorption spectroscopy and thermal desorption spectroscopy. Pt/Ru(0001) has been chosen as a model system to analyze the individual influences of lateral strain and of the residual substrate interaction on the energetics of a dissociative adsorption system. It is found that adsorption and dissociative sticking depends dramatically on Pt film thickness. Even though oxygen adsorption proceeds in a straightforward manner on Pt(111) and Ru(0001), molecular chemisorption of oxygen on Pt/Ru(0001) is entirely suppressed for the Pt/Ru(0001) monolayer. For two Pt layers chemisorbed molecular oxygen on Pt terraces is produced, albeit at a very slow rate; however, no (thermally induced) dissociation occurs. Only for Pt layer thicknesses N(Pt) ≥ 3 sticking gradually speeds up and annealing leads to dissociation of O(2), thereby approaching the behavior for oxygen adsorption on genuine Pt(111). For Pt monolayer films a novel state of chemisorbed O(2), most likely located at step edges of Pt monolayer islands is identified. This state is readily populated which precludes an activation barrier towards adsorption, in contrast to adsorption on terrace sites of the Pt/Ru(0001) monolayer.

Stress analysis of ultra-thin silicon chip-on-foil electronic assembly under bending

In this paper we investigate the bending-induced uniaxial stress at the top of ultra-thin (thickness ⩽20 μm) single-crystal silicon (Si) chips adhesively attached with the aid of an epoxy glue to soft polymeric substrate through combined theoretical and experimental methods. Stress is first determined analytically and numerically using dedicated models. The theoretical results are validated experimentally through piezoresistive measurements performed on complementary metal-oxide-semiconductor (CMOS) transistors built on specially designed chips, and through micro-Raman spectroscopy investigation. Stress analysis of strained ultra-thin chips with CMOS circuitry is crucial, not only for the accurate evaluation of the piezoresistive behavior of the builtin devices and circuits, but also for reliability and deformability analysis. The results reveal an uneven bending-induced stress distribution at the top of the Si-chip that decreases from the central area towards the chipʼs edges along the bending direction, and increases towards the other edges. Near these edges, stress can reach very high values, facilitating the emergence of cracks causing ultimate chip failure.

Adsorption of intact methanol on Ru(0001)

Fourier transform infrared absorption spectroscopy has been used to study the adsorption of methanol on the clean Ru(0001) surface at T<or=80 K. Thereby, clear evidence for intact adsorption has been found. This observation contradicts previous studies which suggested an OH (OD) bond scission upon adsorption of methanol on Ru(0001), even at low temperatures, as well as partial recombinative desorption at higher T. Our conclusion is based on isotopic shifts of vibrational modes associated with the OH (OD) group of adsorbed CH(3)OH and CH(3)OD. Density functional theory (B3LYP) confirms these findings, as it reproduces the observed frequencies and isotopic shifts well. Additional support for our conclusion of nondissociative adsorption of methanol on Ru(0001) is provided by thermal desorption experiments of CH(3)OH coadsorbed with deuterium on Ru(0001). We find that CH(3)OD formation is clearly below detection threshold, while desorption of CH(3)OH is quite prominent; a recombinative desorption of dissociated methanol and hydrogen/deuterium as suggested in the literature is therefore discarded. At very low coverages and temperatures the presence of isolated methanol molecules or dimers is suggested. With increasing density or by annealing a low coverage methanol layer, hydrogen bonding leads to cluster formation, as evidenced by an intensity loss of those vibrational modes affected by hydrogen bonds, in conjunction with a substantial line broadening.

Low-Cost and Durable Bipolar Plates for Proton Exchange Membrane Electrolyzers

Cost reduction and high efficiency are the mayor challenges for sustainable H2 production via proton exchange membrane (PEM) electrolysis. Titanium-based components such as bipolar plates (BPP) have the largest contribution to the capital cost. This work proposes the use of stainless steel BPPs coated with Nb and Ti by magnetron sputtering physical vapor deposition (PVD) and vacuum plasma spraying (VPS), respectively. The physical properties of the coatings are thoroughly characterized by scanning electron, atomic force microscopies (SEM, AFM); and X-ray diffraction, photoelectron spectroscopies (XRD, XPS). The Ti coating (50 μm) protects the stainless steel substrate against corrosion, while a 50-fold thinner layer of Nb decreases the contact resistance by almost one order of magnitude. The Nb/Ti-coated stainless steel bipolar BPPs endure the harsh environment of the anode for more than 1000 h of operation under nominal conditions, showing a potential use in PEM electrolyzers for large-scale H2 production from renewables.

Improving the activity and stability of Ir catalysts for PEM electrolyzer anodes by SnO2:Sb aerogel supports: does V addition play an active role in electrocatalysis?

Low Ir loading oxygen evolution reaction (OER) catalysts with superior activity and durability for proton exchange membrane (PEM) electrolyzers are an important topic in industry and academia. One possible strategy for addressing this challenge is the use of support materials that are stable under highly corrosive acidic environments at a high working potential (>1.4 V). Moreover, highly porous structure is another key criteria for OER catalyst support to achieve a high electrochemical surface area. Here, we report a novel Ir supported on a SnO2:Sb aerogel OER catalyst (Ir/SnO2:Sb-mod-V), which was prepared under ambient pressure by using vanadium additives. It shows an unrivaled activity and enhanced stability, on which vanadium does not play any active role but demonstrates the influences that changes the porosity of the aerogel support and affects the impurity content of the chlorine. By taking advantage of the high porosity of the aerogel substrate, Ir/SnO2:Sb-mod-V allows a decrease of more than 70 wt% for precious metal usage in the catalyst layer while keeping a similar OER activity compared to its unsupported counterpart.

Modification of gas diffusion layers properties to improve water management

In this paper we report an approach to improve water management of commercial GDLs by introducing hydrophobicity patterns. Specifically, line and grid patterns have been created in the MPL side by laser radiation. For an in-depth investigation of these modified GDLs the current density distribution was monitored during fuel cell operation. Additionally, the physical properties of these materials were investigated by a number of ex situ methods such as Fourier transform infrared microscopy, electrochemical impedance spectroscopy and water vapor sorption. Furthermore, a comparison of the physical properties of the patterned GDLs with chemically modified GDLs (treated in H2SO4 and H2O2) is provided. Our results show a clearly improved homogeneity of current density distribution of the patterned GDLs compared to untreated GDLs. This observation is likely due to a reduced local hydrophobicity which facilitates water diffusion along the flow field of the fuel cell. However, performance of the fuel cell was not affected by the MPL irradiation.Graphical Abstract