Hydrogen Diffusion Barrier Research Articles

Nanoscale Proton-Conducting Oxide Membranes for Low Temperature Water Electrolysis

Operating water electrolyzers at higher current densities is an attractive approach to improving the economics of hydrogen production from water electrolysis. Conventional proton exchange membrane (PEM) electrolyzers based on Nafion membranes already operate at relatively high current densities (1.5-2.5 A cm-2), but increasing the current density to 5 A cm-2 or higher would improve the economics even further. Currently, a major limitation of operating low-temperature PEM electrolyzers at such high current densities is the large ohmic drop across the Nafion membrane, which can dramatically lower electrolyzer efficiency. To reduce the membrane resistance and enable efficient operation at high current densities, our team has been exploring the use of nanoscopic proton-conducting silicon oxide (SiOx) membranes. Although the proton conductivity of these oxide membranes is lower than Nafion, we show that their total resistance can be made much lower than conventional Nafion-117 membranes by decreasing their thickness to the nanoscale. The use of sub-micron thick membranes is made possible by the high density of SiOx compared to Nafion, which makes SiOx membranes excellent hydrogen (H2) diffusion barriers for preventing H2 crossover. In this work, we show that the area specific membrane resistance of nanoscale SiOx membranes can be reduced to less than 20% that of Nafion-117 membranes while still maintaining desirable H2 blocking capabilities and avoiding problematic electronic leakage current.

Investigating the impact of alloying elements on hydrogen diffusion in Ti-based alloys via first-principles calculations

The diffusion of hydrogen in Ti-based alloys can lead to localized degradation of mechanical properties, resulting in hydrogen embrittlement. Therefore, identifying alloying elements that impede hydrogen diffusion is a crucial approach to mitigating hydrogen embrittlement and stress corrosion in Ti-based alloys. Utilizing first-principles calculations, we investigated the effects of 33 alloying elements on hydrogen diffusion in Ti-based alloys, including diffusion barriers and coefficients. Our findings demonstrate that elements such as Al, Ga, Si, and Zn increase the hydrogen diffusion barriers and decrease the diffusion coefficients in Ti-based alloys, thereby mitigating hydrogen embrittlement. It is revealed that the difference of electronegativity of Al, Si, Au, Ag, Pd, Ir, Zn, and Cu affects the hydrogen atom trapping ability. It also sheds light on strategies to mitigate hydrogen embrittlement in Ti-based alloys. This insight highlights their significant role in hindering the movement of hydrogen atoms within the alloys.

Vacancy-Induced Anionic Electrons in Single-Metal Oxides and Their Possible Applications in Ammonia Synthesis.

Realizating of a low work function (WF) and room-temperature stability in electrides is highly desired for various applications, such as electron emitters, catalysts, and ion batteries. Herein, a criterion based on the electron localization function (ELF) and projected density of states (PDOS) in the vacancy of the oxide electride [Ca24Al28O64]4+(4e-) (C12A7) was adopted to screen out 13 electrides in single-metal oxides. By creating oxygen vacancies in nonelectride oxides, we find out 9 of them showed vacancy-induced anionic electrons. Considering the thermodynamic stability, two electrides with ordered vacancies, Nb3O3 and Ce4O3, stand out and show vacancy-induced zero-dimensional anionic electrons. Both exhibit low WFs, namely 3.1 and 2.3 eV for Nb3O3 and Ce4O3, respectively. In the case of Nb3O3, the ELF at oxygen vacancies decreases first and then increases during the decrease in the total number of electrons in self-consistent calculations due to Nb's multivalent state. Meanwhile, Ce4O3 displays promise for ammonia synthesis due to its low hydrogen diffusion barrier and low activation energy. Further calculations revealed that CeO with disordered vacancies at low concentrations also exhibits electride-like properties, suggesting its potential as a substitute for Ce4O3.

Atomistic-scale insights into hydrogen diffusion barrier in nickel hydride: Complex interplay between short- and long-range hydrogen arrangement and hydrogen concentration

Metal hydrides, such as those containing Pd, Ni and Mg, are being considered as potential candidates for hydrogen storage applications. The sluggish hydrogen uptake/release in such materials at ambient conditions presents a major issue. The timescales are dictated mainly by diffusion, as it is usually the rate-controlling step. In order to identify practical strategies for improving the kinetics, one must therefore gain an atomistic-scale understanding of the hydrogen diffusion, which is generally lacking from experiments. We address this gap by analyzing the hydrogen hopping mechanism and the associated barriers in two million different hydrogen configurations in NiHx (x = 0–1) using computational techniques. A distribution of hopping barriers is observed. The barriers lie between 0.3–0.7 eV. Three factors, namely, the short- and long-range hydrogen arrangement and the hydrogen concentration influence the barrier. We also show that depending on these factors, two different H hopping mechanisms may prevail. At higher H concentration, the lattice expands by as much as 19 % by volume, making it easier for the hydrogen atom to hop. Therefore, hydrogen diffusion is sluggish in the initial α phase, which may explain the experimentally-observed induction behavior. This study highlights the complexity associated with the metal hydride systems and provides the basis for further molecular scale kinetic studies of metal hydride systems.

Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

AbstractSuperconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride‐based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary‐ion mass spectrometry, X‐ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb2O5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power‐independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two‐level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices.

Hydrogen diffusion dynamics on [formula omitted] surface: A mechanism of hydrogen-induced failure

Hydrogen-induced failure (embrittlement as the primary source) is a significant concern for retrofitting existing pipelines to transport hydrogen. One of the major factors associated with hydrogen embrittlement of metals is hydrogen diffusion. Therefore, understanding the modes and dynamics of hydrogen diffusion into metals is critical for understanding better and acting to limit hydrogen-induced damage to metals. It is well established that transition metals catalyze the dissociation of molecular hydrogen into atomic hydrogen even at room temperature. The atomic hydrogen diffuses through the metal surface, and this causes degradation. Understanding atomic hydrogen diffusion dynamics is critical to reducing hydrogen embrittlement. This work presents atomic hydrogen diffusion dynamics along and into Fe(100) surfaces. The results indicated that diffusion of atomic hydrogen along the surface is favored over surface-to-subsurface diffusion. Once hydrogen diffuses to the subsurface layer, the barrier for further hydrogen diffusion into the subsequent layers is relatively lower. The methodology presented here of atomic hydrogen diffusion under dynamic relaxation into metal surface can be used to study the effect of the metal's chemical composition and structure on the hydrogen diffusion rate. This allows for screening various strategies to reduce hydrogen diffusion into metals and guide the design of degradation prevention strategies.

Innovative Materials and Techniques for Enhancing Hydrogen Storage: A Comprehensive Review of Damage Detection and Preventive Strategies

Abstract Hydrogen is a promising alternative energy resource, but an improvement of secure and efficient storage solutions must be developed for its increased use. This review will investigate efforts to improve the storage of hydrogen using Solid-State methods such as Activated Carbon, Carbon Nanotubes, Metal-Organic Framework, and Metal Hydrides in comparison with traditional liquid and gaseous storage methods. Solid-state methods rely on the temporary trapping or chemical bonding of the hydrogen atoms and molecules to reduce the reactivity and explosivity of the hydrogen and improve safety and equipment sustainability. To support the research into storage methods and improve the industrial infostructure for an increase in hydrogen use, several methods for detecting hydrogen are explored, including Acoustic Emissions Testing, Scanning Kelvin Probe Testing, and Digital Image Correlation. Lastly, various preventative measures used to improve the performance of material used in Hydrogen environments are researched, including Laser Shock Peening, Hydrogen Recombination Coatings, Hydrogen Diffusion Barriers, Hydrogen Getter Coating, and Microstructure Testing.

Superior hydrogen permeation resistance via Ni–graphene nanocomposites: Insights from atomistic simulations

Designing hydrogen-resistant Ni-based alloys from the perspective of the Ni/graphene interface (NGI) provides the potential to increase hydrogen trapping away from potential fracture paths. Nonetheless, numerous essential mechanisms of hydrogen penetration behaviors in the Ni-graphene nanocomposites are presently not well understood. Here we investigate the influence of Ni/graphene interfaces (NGIs) on the behavior of hydrogen diffusion and trapping in their vicinity using atomistic simulations. Hydrogen diffusion is competitively affected by elevated temperatures and NGIs. The difference in the mean square displacement for hydrogen between the composites and pure Ni can be of two orders of magnitude, highlighting the sluggish diffusion in the composites. As NGIs reduce hydrogen formation energy and diffusion barrier, hydrogen prefers to migrate towards the interfaces. Hydrogen readily forms sp3 C–H bonds with C atoms, thereby impeding its detachment from graphene and subsequent entry into a non-diffusible state. Results of the study will contribute to the use of Ni–graphene nanocomposites as hydrogen-resistant materials for nuclear reactors.

Exploring fatigue characteristics of metallic boss-polymer liner adhesion in hydrogen storage tanks: Experimental insights post surface treatment

Progress in hydrogen fuel powered systems has been propelled by the implementation of secure, reliable, and cost-effective hydrogen storage and transportation technologies. The fourth category, distinguished by a polymer liner serving as a hydrogen diffusion barrier, fully encapsulated within a fiber-reinforced composite to bestow structural integrity, has garnered substantial attention from the automotive industry due to its lightweight nature and rational manufacturing process. The method of rotomolding has sparked interest among manufacturers due to its capability to directly bond the metallic component to the polymer substrate, specifically the liner, thus negating the need for welding and its attendant imperfections. In fact, a pivotal facet of fourth-generation hydrogen storage systems revolves around the interface connection between the polymer liner and the metallic boss, posing as a structural Achilles' heel. For the study's purposes, a scaled-down demonstrator was fabricated using rotomolding in which a nozzle-liner interface mimics the boss-liner interface of the actual system. This demonstrator was designed to facilitate the mechanical characterization of the interface under quasi-static and fatigue loading. The thermal cycling phases of rotational molding and the surface treatments undertaken have been optimized in order to enhance direct adhesion within the metal-polymer interface. This study commences by assessing the efficacy of two treatments (sandblasting and flaming) applied to the aluminum nozzle surface. Subsequently, we explore the adhesion microstructural and mechanical characteristics of the treated nozzle onto a medium-density polyethylene polymer (liner). Lastly, we delve into an exploration of the damage and fatigue behaviors endemic to the metal-polymer interface region. The obtained Wöhler curves disclose a linear trend for the metal-polymer interface. Moreover, the metal-polymer interface evinces heightened resilience against damage and fracture for sandblasted interfaces. This inquiry underscores the potency of innovative polymer-metal interfaces treatment in amplifying the reliability and robustness of hydrogen storage technology.

The anionic Tx defects of Nb2CTx MXene as the effective catalytically active center for the Mg-based hydrogen storage materials

While early transition metal-based materials, such as MXene, has emerged as an efficient catalyst for the Mg-based hydrogen storage materials, their strong interaction with hydrogen resulted in the high hydrogen diffusion barrier, hindering further improvement of catalytic activity. A MXene is characterized by rich anionic groups on its surface, significantly affecting electronic and catalytic functionalities. Using Nb2CTx as an example, we herein illustrate the critical role of anionic Tx defects on controlling hydrogen dissociation and diffusion processes in Mg-based hydrogen storage materials. The hydrogen desorption properties of MgH2 can be significantly enhanced by utilizing Tx controllable Nb2CTx, and it can release 3.57 wt.% hydrogen within 10 min under 240 °C with the reduced dehydrogenation activation barrier. It also realized stable de/hydrogenation reactions for at least 50 cycles. DFT studies combined with kinetic analysis revealed that the catalyst‒hydrogen interaction could be systematically controlled by optimizing surface Tx defect density, accelerating the hydrogen dissociation and diffusion processes at the same time. These results demonstrate that the Tx defects serve as the effective catalytically active centers of Nb2CTx, offering a flexible catalyst design guideline.

Designing functionalized graphene-stitched-SiC/fluoropolymer novel composite coating with excellent corrosion resistance and hydrogen diffusion barrier properties

The investigation on ordinary hydrogen barrier composite coatings has been limited in terms of corrosion and high-pressure hydrogen environments, which significantly restricts its practical and industrial applications. Herein, a unique nanohybrid two-dimensional (2D) filler, constituting poly-dopamine (PDA) functionalized graphene (Gr) nanosheets and covalently bridged silicon carbide (SiC) nanoflakes assisted by 3-Isocyanatopropyltrimethoxysilane (IPTMS) via hydrolysis reaction, was innovatively proposed and incorporated into fluoroethylene vinyl ether resin (FEVE) to fabricate final composite coating by spin-coating technique. The hydrogen gas barrier and long-term anti-corrosion performances could be simultaneously enhanced by precisely collaborative effects of interfacial interactions fortification among Gr, SiC, and polymer phase as well as centrifugal force promoted Gr orientation during the spinning process. The optimum sample demonstrated high |Z|0.01Hz values of 3.1 × 1011 Ω cm2 and 3.37 × 1011 Ω cm2 throughout 90 d saltwater immersion and 6-day 1.5 MPa pressurized hydrogen environment exposure respectively. Moreover, its permeability coefficient decreased by 75.66% compared to the pure sample. Other significant properties including 30d constant salt-spray attack tolerance and high adhesion strength of 12.46 MPa were also achieved to meet industrial demands. This work provided paramount inspiration for designing composite coatings for hydrogen transportation pipeline protection and hydrogen energy usage.

Theoretical Methods of Hydrogen Diffusion Calculation in Metals Review

In the review discuss some theoretical methods of hydrogen diffusion calculation in metals. True values of the energy barrier for hydrogen diffusion can be calculated from first principles. The transition from the theoretical values of the energy barrier to the model values of the activation energy is associated with considering additional influencing factors, primarily physical parameters – zero-point energy, decay of local deformation near the hydrogen atom, temperature-dependent potentials, etc. The presentation of the results is greatly influenced by the parameters of the diffusion models used for calculations - the Arrhenius equation, the Einstein formula of molecular dynamics, the Kerr diffusion equation, the operator expression of quantum statistical mechanics, and diffusion equation of statistical thermodynamics. The statistical model of H diffusion in FCC metals at a high temperature makes it possible to explain the high values of the pre-exponential factor of H diffusion coefficients. The results of many works show that quantum effects play a decisive role in the H diffusion in metals at low temperatures. Further development of quantum- mechanical theories of diffusion will allow for consideration of the influence of these factors.

Understanding hydrogen diffusion mechanisms in doped α-Fe through DFT calculations

Hydrogen embrittlement is detrimental to structural metals during applications. Herein, we explore the hydrogen diffusion mechanisms in doped α-Fe using first-principles calculations. We prove that the hydrogen trap is a thermodynamically spontaneous process, and doping will decrease the hydrogen adsorption energy due to the change of adsorption sites. Furthermore, hydrogen diffusion from surface to subsurface will determine the diffusion rate. Mo, Mn and C are beneficial to the increase of the energy barrier of hydrogen diffusion from the surface to subsurface and in the bulk. The current work provides a promising path towards enhancing the hydrogen diffusion barrier in α-Fe.

Thermal desorption study on possible hydrogen sources and diffusion barriers in CMOS technology

Hydrogen passivation of silicon dangling bonds is a key requirement in the realization of reliable CMOS devices. The creation of a hydrogen reservoir in the device near the silicon may be a solution supporting constant passivation during the life-cycle of the device. In this work, we used thermal desorption spectroscopy to evaluate the amount of hydrogen stored in undoped silicon glass (USG) deposited using SiH4 (USG-SiH4) or tetraethyl orthosilicate (USG-TEOS), and silicon (carbon) nitrides, typical dielectrics used in CMOS technology. The goal of the study is to determine if these materials can be used as hydrogen source or diffusion barrier. Our results suggest that USG-SiH4 can act as an efficient source of hydrogen, while Si nitrides can act as reliable diffusion barrier.

Unraveling the substitution and strain-induced hydrogen diffusion performance of ZrCo-based intermetallics

The intermetallic compound zirconium-cobalt (ZrCo) is one of promising alternative materials used in the industry of hydrogen isotope storage. Nevertheless, the deterioration of absorption/desorption kinetics induced by hydrogen-induced disproportionation severely impedes its large-scale promotion. This work concentrates on studying the hydrogen diffusion behavior of ZrCo hydrides due to element substitution combined with triaxial strain (−3% ∼ 3 %) under the framework of the first-principles study. The results indicate that the formation of small-volume hydrogen vacancies is facilitated by Ti substitution as well as compressive strain. Moreover, hydrogen diffusion barrier is reduced after the Ti substitution, leading to a significant increase in diffusion rate. When the Ti content reaches 15 %, it is more conductive to improving the dehydrogenation kinetics of hydride. As the compressive strain increases, the diffusion barrier is reduced to a minimum at −3%. In addition, the Ti substitution and strain play a synergistic effect for enhancing hydrogen diffusion rate. Also, it is found that the performance of hydrogen diffusion and dehydrogenation kinetics is attributed to lattice stability associated with the density of states at the Fermi level. This work provides a new insight to improve dehydrogenation kinetics of ZrCoH3 by taking into account element substitution and external strain.

Compact Integration of Hydrogen–Resistant a–InGaZnO and Poly–Si Thin–Film Transistors

The low–temperature poly–Si oxide (LTPO) backplane is realized by monolithically integrating low–temperature poly–Si (LTPS) and amorphous oxide semiconductor (AOS) thin–film transistors (TFTs) in the same display backplane. The LTPO–enabled dynamic refreshing rate can significantly reduce the display’s power consumption. However, the essential hydrogenation of LTPS would seriously deteriorate AOS TFTs by increasing the population of channel defects and carriers. Hydrogen (H) diffusion barriers were comparatively investigated to reduce the H content in amorphous indium–gallium–zinc oxide (a–IGZO). Moreover, the intrinsic H–resistance of a–IGZO was impressively enhanced by plasma treatments, such as fluorine and nitrous oxide. Enabled by the suppressed H conflict, a novel AOS/LTPS integration structure was tested by directly stacking the H–resistant a–IGZO on poly–Si TFT, dubbed metal–oxide–on–Si (MOOS). The noticeably shrunken layout footprint could support much higher resolution and pixel density for next–generation displays, especially AR and VR displays. Compared to the conventional LTPO circuits, the more compact MOOS circuits exhibited similar characteristics.

Reaction barriers on non-conducting surfaces beyond periodic local MP2: Diffusion of hydrogen on α-Al2O3(0001) as a test case.

The quest for "chemical accuracy" is becoming more and more demanded in the field of structure and kinetics of molecules at solid surfaces. In this paper, as an example, we focus on the barrier for hydrogen diffusion on a α-Al2O3(0001) surface, aiming for a couple cluster singles, doubles, and perturbative triples [CCSD(T)]-level benchmark. We employ the density functional theory (DFT) optimized minimum and transition state structures reported by Heiden, Usvyat, and Saalfrank [J. Phys. Chem. C 123, 6675 (2019)]. The barrier is first evaluated at the periodic Hartree-Fock and local Møller-Plesset second-order perturbation (MP2) level of theory. The possible sources of errors are then analyzed, which includes basis set incompleteness error, frozen core, density fitting, local approximation errors, as well as the MP2 method error. Using periodic and embedded fragment models, corrections to these errors are evaluated. In particular, two corrections are found to be non-negligible (both from the chemical accuracy perspective and at the scale of the barrier value of 0.72eV): the correction to the frozen core-approximation of 0.06eV and the CCSD(T) correction of 0.07eV. Our correlated wave function results are compared to barriers obtained from DFT. Among the tested DFT functionals, the best performing for this barrier is B3LYP-D3.

Understanding Light- and Elevated Temperature-Induced Degradation in Silicon Wafers Using Hydrogen Effusion Mass Spectroscopy

Hydrogen has been long known for its ability to passivate defects in silicon devices. However, multiple recent studies on understanding the mechanism behind light- and elevated temperature-induced degradation (LeTID) have proposed that hydrogen plays an important role in this degradation mechanism. Despite its important role in photovoltaic applications, the quantitative assessment of hydrogen is difficult and seldom reported. In this work, we applied hydrogen effusion mass spectroscopy to quantify the hydrogen released from hydrogenated silicon nitride (SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H) and atomic layer deposited (ALD) aluminum oxide (AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) dielectric films at elevated temperatures. We demonstrate that the amount of hydrogen effused from these layers strongly correlates with the extent of LeTID observed in the multicrystalline silicon wafers passivated with these monolayers and their stacks. It is shown that the hydrogen effusion scales linearly with the SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H thickness, similar as the extent of LeTID. The effusion measurements on the AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H stack revealed that the presence of the AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> film modifies the total amount of hydrogen that is effused, whereas it was found to slow the hydrogen in-diffusion. This result is consistent with the LeTID extent determined after contact firing where ALD AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layers were found to act as a hydrogen diffusion barrier, strongly reducing LeTID when placed in between c-Si and SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H and increasing LeTID when placed on top of SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H.

Impact of hydrogen on the boron-oxygen-related lifetime degradation and regeneration kinetics in crystalline silicon

We examine the impact of hydrogen on the boron-oxygen-related lifetime degradation and regeneration kinetics in boron-doped p-type Czochralski-grown silicon wafers. We introduce the hydrogen into the silicon bulk by rapid thermal annealing. The hydrogen source are hydrogen-rich silicon nitride (SiNx:H) layers. Aluminum oxide (Al2O3) layers of varying thickness are placed in-between the silicon wafer surfaces and the SiNx:H layers. By varying the Al2O3 thickness, which acts as an effective hydrogen diffusion barrier, the hydrogen bulk content is varied over more than one order of magnitude. The hydrogen content is determined from measured wafer resistivity changes. In order to examine the impact of hydrogen on the degradation kinetics, all samples are illuminated at a light intensity of 0.1 suns near room temperature. We observe no impact of the in-diffused hydrogen content on the degradation rate constant, confirming that hydrogen is not involved in the boron-oxygen degradation mechanism. The regeneration experiments at 160°C and 1 sun, however, show a clear dependence on the hydrogen content with a linear increase of the regeneration rate constant with increasing bulk hydrogen concentration. However, extrapolation of our measurements toward a zero in-diffused hydrogen content shows that the regeneration is still working even without any in-diffused hydrogen. Hence, our measurements demonstrate that there are two distinct regeneration processes taking place. This is in good agreement with a recently proposed defect reaction model and is also in agreement with the finding that the permanent boron-oxygen deactivation also works on non-fired solar cells, though at a lower rate.

Thermal activation of hydrogen for defect passivation in poly-Si based passivating contacts

Hydrogenation of poly-Si based passivating contacts (TOPCon) is an essential process to achieve a very high level of surface passivation, especially on textured surface. This contribution is dedicated to improve the understanding of the hydrogenation mechanism. We compare different hydrogen sources with regard to their ability to chemically passivate defects at the Si/SiO x interface and presumably in the doped poly-Si layer as well as their thermal stability in a low and high temperature range. To this end, hotplate annealing series were performed on textured n -type TOPCon structures and Al 2 O 3 /SiN x multi-layer stacks were exposed to fast-firing processes. Very distinct activation characteristics were detected. It was also observed that the Al 2 O 3 capping layers enable a higher level of surface passivation and higher thermal stability compared to SiN x . When implemented in multi-layer stacks, Al 2 O 3 acts as a hydrogen diffusion barrier und prevents effusion from the TOPCon structure that deteriorates the passivation quality irreversibly. • Hydrogenation of poly-Si based passivating contacts. • Thermal activation of hydrogenation. • Hydrogenation of TOPCon using AlOx/SiNx stacks. • Thermal stability of hydrogenation upon fast-firing.