Enhancing the durability of Pt nanoparticles for water electrolysis using ultrathin SiO₂ layers

Abstract

Extending the lifetime of electrocatalytic materials is a major challenge in electrocatalysis. Here, we employ atomic layer deposition (ALD) to coat the surface of carbon black supported platinum nanoparticles (Pt/CB) with an ultra-thin layer of silicon dioxide (SiO₂) to prevent deactivation of the catalyst during H₂ evolution. Our results show that after an accelerated durability test (ADT) the current density at −0.2 V vs. reversible hydrogen electrode (RHE) of the unprotected Pt/CB catalyst was reduced by 34%. By contrast, after coating the Pt/CB catalyst with 2 SiO₂ ALD cycles, the current density at the same potential was reduced by 7% after the ADT procedure, whereas when the Pt/CB sample was coated with 5 SiO₂ ALD cycles, the current density was reduced by only 2% after the ADT. Characterization of the Pt particles after electrochemical testing shows that the average particle size of the uncoated Pt/CB catalyst increases by roughly 16% after the ADT, whereas it only increases by 3% for the Pt/CB catalyst coated with 5 cycles of SiO₂ ALD. In addition, the coating also strongly reduces the detachment of Pt nanoparticles, as shown by a strong decrease in the Pt concentration in the electrolyte after the ADT. However, 20 cycles of SiO₂ ALD coating results in an over-thick coating that has an inhibitory effect on the catalytic activity. In summary, we demonstrate that only a few cycles of SiO₂ ALD can strongly improve the stability of Pt catalyst for the hydrogen evolution reaction.

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Introduction

Hydrogen is a pivotal feedstock for the chemical industry and is one of the pillars of the energy transition, as it is a clean and sustainable energy carrier.¹ Currently, the most widely used method for hydrogen production is natural gas reforming, which emits large amounts of CO₂, relies on fossil inputs, and produces blue or grey hydrogen. When integrated with renewable electricity production, water electrolysis yields nearly no CO₂ emissions during operation and produces green hydrogen.² Platinum (Pt) is one of the most effective electrocatalysts for both water reduction to hydrogen in polymer electrolyte membrane (PEM) electrolyzers and hydrogen oxidation in PEM fuel cells. However, as a noble metal, its high costs and scarcity limit its application.

To overcome these challenges, most of the research focusses on two potential solutions. The first approach is to decrease the Pt amount in the electrolyzer and improve the Pt utilization efficiency via decreasing the Pt particle size. For instance, Wan et al.³ confined sub-nanometer Pt clusters in hollow mesoporous carbon spheres to stabilize and immobilize the Pt clusters, enhancing the mass activity of the Pt catalyst. Additionally, Cheng et al.⁴ produced isolated single Pt atoms and clusters on a N-doped graphene substrate using atomic layer deposition (ALD) and found that these have a higher activity compared to commercial Pt/C catalysts. This is due to their small sizes and the unique electronic interaction between the adsorbed Pt single atoms and N-doped graphene. The second approach is to protect the Pt catalyst from degradation and prolong its lifetime. The Pt catalysts used for water electrolysis mainly degrade via dissolution, catalyst detachment, and agglomeration processes as deactivation mechanisms.^1,5 Marichy et al.⁶ combined electrospinning, microwave-assisted synthesis, and ALD to synthesize Pt nanoparticles on carbon fibers with a SnO₂ coating. They found that with the SnO₂ coating, the Pt catalyst durability increased remarkably during voltage cycling between 0.6 V and 1.2 V vs. reversible hydrogen electrode (RHE) and that the activity towards the oxygen reduction reaction (ORR) increased slightly. The SnO₂ layer lowered the corrosion of the carbon support and prevented the aggregation of Pt particles. Kim et al.⁷ found that a TiO₂ coating can be used to enhance the activity and stability of Co/C catalysts for electrochemical water oxidation. The TiO₂ coating can prevent the catalyst from sintering as it decorates the undercoordinated Co nanoparticles at defects, corners, and edges, protecting those sites. However, the intrinsic instability of these metal oxides coatings remains a concern when they are applied for protection under reductive potentials.⁸

SiO₂ is stable under acidic (pH ≥ 2) as well as moderately alkaline (pH ≤ 10) conditions, and exhibits outstanding electrochemical stability under both reductive and oxidative potentials.^9,10 Its high-temperature resistance is also outstanding, allowing it to remain stable up to 650 °C.^11,12 This makes it a suitable material for catalyst protection and therefore it is already used for the protection of catalysts in thermochemical and photochemical processes. For example, Wang et al.¹³ used SiO₂ to introduce a strong metal–support interaction with Cu catalysts and to stabilize these catalysts for hydrogenation reactions. Li et al.¹⁴ applied SiO₂ to encapsulate cobalt oxide nanoparticles used as methane combustion catalyst. They found that the embedded CoO_x@SiO₂ catalyst showed superior performance compared to the bare supported CoO_x@SiO₂ catalyst. Trompoukis et al.¹⁵ used SiO₂ to protect a Pt photocatalyst and found that the SiO₂ can increase the minority carrier lifetimes and avoids the growth of thin interfacial oxide between the photoactive material and the catalyst. Takenaka et al.¹⁶ used an impregnation method to deposit different amounts of SiO₂ on a Pt/CB electrocatalyst to increase the durability of this catalyst in a polymer electrolyte fuel cell (PEFC). However, due to the impregnation method they used, the lowest SiO₂ coating loading achieved in the catalyst is 12.5 wt%, which, while considered low, still represents a relatively high percentage. While the durability of the catalyst used at the cathode is increased, the relatively thick SiO₂ coating decreases the Pt/CB catalyst activity. Since SiO₂ is more insulating than the metal oxides mentioned before, minimizing the coating thickness is crucial to maintain the electrical conductivity of the catalyst during electrocatalysis to avoid inactivate the catalyst. As such, very thin insulator films (thickness of <2 nm) are still conductive due to the tunneling effect, while very thick coatings will have a suppressive effect on the catalytic activity.^17,18 To achieve a uniformly covered surface of the catalyst with an ultrathin coating, a gentle and delicate method with precise control at the nanometer scale is required. ALD is a suitable choice due to its sub-nanometer control over layer thickness, enabling the production of uniform and conformal coatings on various surfaces.¹⁹ Furthermore, investigating the impact of the SiO₂ coating on the water splitting, rather than application in a PEFC, is also necessary.

In this work, we demonstrate the potential of ultrathin SiO₂ coatings made via ALD to enhance the stability of commercial Pt on carbon black (Pt/CB) catalysts for the hydrogen evolution reaction. We find that an ultrathin SiO₂ coating can efficiently provide a strongly protective effect, preventing the catalyst from agglomeration and detachment in accelerated durability tests (ADT). While the thickness of the protective layer has a stronger effect on catalyst performance than was previously recognized.

Experimental section

Materials

Silicon tetrachloride (SiCl₄, 99%) was purchased from Alfa Aesar, isopropanol (≥98%) was purchased from Honeywell, Nafion™ perfluorinated resin solution (5 wt% in lower aliphatic alcohols and 15–20% water) and sulfuric acid (H₂SO₄, 95–97%) were purchased from Sigma-Aldrich. Deionized water with the resistivity of 18.2 MΩ were used as the co-reactant. 40 wt% of Pt on carbon black – Vulcan XC 72R catalyst was purchased from the FuelCell store. Glassy carbon rods and glassy carbon plates were ordered from HTW Hochtemperatur-Werkstoffe GmbH (Germany). The electrolyte solution was prepared from ultrapure water (Milli-Q IQ 7000, 18.2 MΩ). All chemicals were received and used without further purification.

Catalyst synthesis

The SiO₂ coatings on the catalyst were deposited in a custom-built flat substrate ALD reactor^19–21 operating at atmospheric pressure. The reactor chamber consists of a metal cylinder with an inner diameter of 40 mm and a length of 190 mm, along with a substrate holder with dimensions of 30 mm by 125 mm. The deposition temperature was monitored and controlled using two thermocouples installed inside and outside wall of the ALD reactor to ensure an even temperature profile. We employed atmospheric pressure ALD here instead of vacuum ALD since at large scale it will reduce the investment costs and increase the throughput.^20,21 The ALD procedure of SiO₂ deposition is modified from the reported literature.²² Nevertheless, the time settings of the reaction and the precursor gas flow rate we used were different. In brief, SiCl₄ and H₂O serving as ALD reactants were kept in stainless-steel bubblers and evaporated at room temperature. N₂, with a purity of 99.999%, was utilized as both the carrier and purging gas, and a gas flow of 0.5 L min⁻¹ was used throughout the whole process. The gas flowed parallel to the surface of the substrate in the reactor. The samples were pre-treated under air plasma at room temperature and at 4 mbar pressure for 60 seconds using a Harrick plasma machine before each experiment. The ALD reactor was heated and maintained at 100 °C for the entire ALD process. 15 seconds pulses were used to introduce SiCl₄ into the reactor, followed by 60 seconds purging with N₂ and 30 seconds dosing of H₂O vapor. After that, 60 seconds purging with N₂ was used to finish a full ALD cycle. More detailed information on SiO₂ ALD operation conditions can be found in Table S1.† Samples with different numbers of ALD cycles were obtained by repeating the ALD cycles for the required times. At the end of synthesis process, the reactor was purged with N₂ flow for 15 minutes and cooled down to room temperature.

Material characterization

The JEOL JEM1400 transmission electron microscope (TEM) operating at 120 kV voltage was employed to examine and analyze the microstructures and particle size distribution of various catalysts. To assess the crystal structure of the catalysts, X-ray diffraction (XRD) measurements were conducted utilizing a Bruker D8 advance diffractometer with Bragg–Brentano geometry and a Lynxeye position-sensitive detector. The X-ray was generated using Cu Kα radiation at 45 kV and 40 mA. The Pt concentration in the electrolyte was quantified using the inductively coupled plasma-optical emission spectrometry (ICP-OES) method, employing a PerkinElmer Optima 5300 DV ICP-OES instrument. X-ray photoelectron spectroscopy (XPS) measurements were performed employing a Thermo Scientific™ K-alpha™ (ThermoFisher™ Scientific) utilizing a monochromated X-ray of aluminum Kα radiation (1486.7 eV) with a spot size of 400 μm. For survey scans, a pass energy of 200 eV and a step size of 1 eV were used, while the high-resolution spectra were acquired with a pass energy of 50 eV and a step size of 0.1 eV. All peak positions were analyzed and calibrated, referencing the aliphatic C1s peak at 284.8 eV, using CasaXPS.

Electrochemical measurements

The electrochemical measurements were conducted using a H-cell setup.²³ The preparation of the working electrodes involved a drop-casting technique. Initially, a catalyst ink was created by mixing 4 mg of catalyst with 800 μL of deionized water, 150 μL of isopropanol, and 50 μL of Nafion perfluorinated resin solution. The mixture was sonicated in an ice bath for 1 hour. Subsequently, 50 μL of the catalyst ink was drop cast onto the glassy carbon electrode surface, repeating the process 4 times. The prepared working electrodes were coated with SiO₂ using the ALD process, as described earlier, and subsequently used as working electrode. An Ag/AgCl electrode served as the reference electrode, while a graphite rod was utilized as the counter electrode. All potentials used in this work were converted to the RHE scale according to the equation:²⁴

E_RHE = E_Ag/AgCl + 0.197 + 0.059 × pH

0.5 M H₂SO₄ was used as electrolyte in both chambers. A cation-exchange membrane, Nafion™ 117 (FuelCell store), was utilized to separate the anode and cathode chamber of the H-cell. A Biologic SP-200 potentiostat was employed to conduct the electrochemical measurements. Potentiostatic electrochemical impedance spectroscopy was used to measure the ohmic loss of the cell and was compensated for every experiment. An ADT was carried out by repeating CV scans for 1000 times between −0.2 V- 0.35 V vs. RHE at a scan rate of 50 mV s⁻¹.²³ Linear sweep voltammetry (LSV) was recorded from −0.3 V to 0 V vs. RHE at a scan rate of 2 mV s⁻¹.

Results and discussion

A series of SiO₂-coated Pt/CB samples was prepared using ALD and compared with the uncoated Pt/CB sample. The deposition procedure used to prepare the coated samples can be found in the experimental section and Table S1.† In summary, the SiCl₄ vapor in a nitrogen stream and a humidified nitrogen stream was alternatingly fed into the home-built tubular flat substrate reactor²⁵ to initiate the layer by layer growth of SiO₂ on the surface of Pt/CB catalyst. By varying the number of coating cycles of the ALD process, the film thickness was changed accordingly. As can be seen in Fig. 1, the TEM images of the original Pt/CB catalyst indicate Pt nanoparticles of 3.2 ± 0.5 nm (number-averaged diameter ± standard deviation). Fig. 1 also shows that the average Pt particle size after SiO₂ ALD does not change considerably. The average Pt size measured through TEM imaging remains 3.2 ± 0.5 nm and 3.2 ± 0.6 for the sample with 5 and 20 ALD cycles, respectively. Considering the reported growth per cycle of SiO₂ using SiCl₄ in the employed experimental conditions, which is around 2 Å per cycle,^26,27 a very thin SiO₂ layer is expected even after 20 cycles of ALD coating. We have conducted the TEM characterization towards the outmost layer of the 20 cycles ALD coated sample, as shown in Fig. S1.† The film thickness of this sample is around 5.8 nm after 20 cycles ALD. This leads to an estimated growth per cycle for SiO₂ of 2.9 Å.

Fig. 1 TEM images and particle size distribution of Pt/CB catalysts before and after SiO₂ ALD coating: (a and d) original Pt/CB without ALD coating; (b and e) Pt/CB catalyst after 5 cycles of SiO₂ ALD coating, and (c and f) Pt/CB catalyst after 20 cycles of SiO₂ ALD coating.

X-ray diffraction (XRD) analysis of the original Pt/CB catalyst and of the Pt/CB catalyst after applying a variant number of ALD cycles of SiO₂ coating were carried out to investigate the crystallinity of the catalysts. Fig. S2† shows that there is no significant distinction between the samples before and after SiO₂ ALD. Two strong carbon peaks are observed in the diffractogram, whereas the Pt signal is relatively weak and only a small peak at 39.8° that represents the Pt(111) plane is observed. SiO₂ peaks were not detected, as is expected since the SiO₂ grown by ALD is mostly amorphous.²⁸

The uniform deposition of SiO₂ on the surface of the catalyst is confirmed with SEM-EDS (Fig. 2). The color bar on the left side of the SEM-EDS maps (Fig. 2a–c) is an indicator of the Si K_α signal intensity in each sample. The SEM-EDS maps indicate that the surface concentration of Si increases with an increase in ALD cycles. It is worth noting that the EDS spectra also reveal a small peak of fluorine which originates from the Nafion™ polymer used as binder to stabilize the catalyst on the surface of the glassy carbon during the drop-casting process. XPS was employed to investigate the surface chemistry of the ALD coated Pt/CB samples. The Si 2p high-resolution spectra (Fig. S3†) suggest that Si in the studied samples exist in the SiO₂ state and can be deconvoluted into Si 2p_3/2 and Si 2p_1/2. The Pt 4f peak intensity slightly diminishes as the number of ALD cycles increases from 2 to 5 cycles (Fig. 3a). However, it becomes vanishingly low after 20 cycles. This indicates a significant coating thickness of SiO₂ after 20 cycles of ALD, which is further supported by the peak intensity of Si shown in Fig. 3b. The Si peak intensity exhibits a slight increase as the number of ALD cycles increases, with a sharp rise after 20 ALD cycles. The analysis depth of XPS is about 4 nm,^29,30 and having a thicker SiO₂ film can strongly attenuate the signal underneath. The very weak Pt 4f peak in the sample coated with 20 ALD cycles compared to the bare sample suggests that the SiO₂ film is above 4 nm. In Fig. S4,† the SiO₂ growth rate was characterized by XPS and EDS, respectively. Due to the detection depth variation of these two techniques,³¹ Fig. S4† shows different Si atomic percentages on the surface of the identical sample. However, both characterizations methods show a monotonic increase of the Si atomic percentage as a function of ALD cycles applied.

Fig. 2 SEM-EDS elemental mapping of the Pt/CB catalysts after SiO₂ ALD coating, the color bar indicates the Si K_α signal intensity in each sample: (a–c) SEM images of Pt/CB catalysts after 2, 5, and 20 cycles of SiO₂ ALD coating; (d and e) EDS spectra of Pt/CB catalysts with and without 20 cycles of SiO₂ ALD coating.

Fig. 3 The Pt and Si XPS spectra of the Pt/CB catalyst with and without SiO₂ coating: (a) Pt 4f XPS spectra, (b) Si 2p XPS spectra.

XPS line scanning was conducted to investigate the SiO₂ uniformity on the catalyst surface. Photoelectron signals were collected from the scanning line through the whole catalyst region, extended to the bare surface of the glassy carbon substrate, and plotted as the function of the horizontal distance. As can be seen from Fig. 4, the surface concentration of Pt 4f, Si 2p, and O 1s reveals a step increase and decrease, indicating the region where the catalyst is drop casted.

Fig. 4 XPS line scan profiles of Pt/CB catalyst after SiO₂ ALD coating: (a) 2 ALD cycles, (b) 5 ALD cycles, and (c) 20 ALD cycles of SiO₂ coating.

The Si 2p and O 1s signals follow the trend of the Pt 4f signal along the line. The C 1s signal shows a trough in the catalyst spot region, stemming from the emerging SiO₂ coverage and the higher Pt atomic percentage in the catalyst region. The Si concentration on the surface of the drop casted catalyst area is significantly higher than on the bare glassy carbon substrate at the edges and increases with the number of ALD cycles. A similar trend can also be seen for the O 1s signal. This observation suggests that the SiO₂ growth rate is much higher on the catalyst surface than on the glassy carbon substrate, and results in selective deposition of SiO₂ on the surface of the Pt/CB catalyst. Two crossover XPS line scans in every sample show comparable results in the X and Y axis, indicating the homogeneity of the catalyst region on the glassy carbon substrate (see Fig. S5†).

To further investigate the SiO₂ distribution on the catalyst area and the glassy carbon substrate, XPS area scans were conducted (Fig. S6 and S7†). The area scan reveals that Pt is homogeneously dispersed over the catalyst region and there is no Si signal detected on the surface of the original Pt/CB catalyst (Fig. S6†). After 5 SiO₂ ALD cycles, the Si 2p signal is clearly visible in Fig. S7† and aligns with Pt/CB region. This again indicates selective deposition of SiO₂ on the catalyst surface rather than on the glassy carbon substrate.

The effect of different thicknesses of SiO₂ coating on the Pt stability during electrochemical hydrogen evolution was evaluated in a H-cell using a 0.5 M H₂SO₄ electrolyte. ADT of the catalysts were conducted similar to literature procedures.^32,33 In brief, cyclic voltammograms were recorded with a scan rate of 50 mV s⁻¹ from 0.35 V to −0.20 V vs. RHE for 1000 cycles. Linear sweep voltammograms (LSV) were recorded before and after the ADT to measure the catalytic activity of the electrode toward hydrogen evolution (Fig. 5). For the Pt/CB catalyst without ALD coating, the current density at −0.20 V vs. RHE was reduced by 34% in the water reduction potential range after the ADT. By contrast, the catalyst coated with 2 ALD cycles of SiO₂ showed a current density reduction at the same voltage of only 7% after the same ADT procedure. After applying 5 cycles of SiO₂ ALD, the catalyst current density was merely reduced by 2% after the ADT. The Nyquist plots shown in Fig. S8† indicate that the charge transfer resistance between the catalysts with and without 5 cycles of ALD coating is comparable. This means that the SiO₂ coating didn't hinder the proton transfer to the Pt catalyst within 5 cycles of ALD coating. However, 20 cycles of SiO₂ deposition showed an inhibitory effect on the catalytic activity, with a 65% decrease in the HER activity compared to the uncoated sample. This indicates that 20 cycles of ALD results in a too thick SiO₂ layer, possibly hindering the electron transfer and suppressing the HER. However, the HER activity of the sample coated with 20 ALD cycles of SiO₂ increased 94% post ADT. Zhuravlev³⁴ summarized that the surface hydroxyl groups in SiO₂ can form due to the rehydroxylation of SiO₂ in aqueous solutions, and the surface SiO₂ atoms' free valence tend to become saturated with hydroxyl groups in aqueous medium. This process can also happen on our SiO₂ layer, especially during the ADT process. Kang et al.³⁵ reported that the silicon hydroxide deposited on the surface of anion-exchange membrane can drastically increase the proton transport number in the membrane. We hypothesize that the increase of silanol groups on the surface of SiO₂ during ADT helps to improve proton transfer in relatively thick SiO₂ layers. Consequently, this process partially restores the HER activity and increases the current density of the 20 cycles coated sample after the ADT procedure.

Fig. 5 Linear sweep voltammogram (LSV) curves of the Pt/CB catalysts before and after accelerated durability tests: (a) original catalyst, Pt/CB catalyst coated with SiO₂ using (b) 2 ALD cycles, (c) 5 ALD cycles, and (d) 20 ALD cycles.

The particle size distribution (PSD) analysis (shown in Fig. 6) of Pt/CB catalysts before and after the ADT tests demonstrates that the average particle size of the Pt/CB catalyst without ALD coating increased from 3.2 ± 0.5 nm to 3.7 ± 0.7 nm after the ADT, an increase of 16%. In comparison, the particle size of the Pt particles only increased from 3.2 ± 0.5 nm to 3.3 ± 0.6 nm after being protected by 5 cycles of SiO₂ ALD coating, an increase of 3% after the ADT. This proves that the SiO₂ coating prevents catalyst growth/agglomeration during the ADT, which is one of the main deactivation mechanisms of Pt electrocatalysts during water electrolysis. Fig. S9† further displays the Pt particle size evolution from TEM imaging after the ADT. Also, Fig. S10 and S11† show that without SiO₂ ALD coating, the bare Pt/CB catalyst surface becomes rougher, and cavities can be seen on the catalyst surface. However, with SiO₂ ALD, the surface of the catalyst before and after the ADT remains nearly similar. The electrolyte after the ADT was collected and analyzed by ICP-OES to measure the Pt concentration in the electrolyte before and after the ADT, and the resulting data is summarized in Table 1. Before the ADT, the Pt concentration in the electrolyte is near 0 mg L⁻¹. During the ADT, the Pt/CB catalyst gradually degrades, and we observed an increase in Pt concentration to 8.9 mg L⁻¹ in the Pt/CB sample without ALD coating after ADT. However, after applying 2 cycles of SiO₂ ALD, the Pt concentration in the electrolyte reduced to 4.1 mg L⁻¹ post ADT. Applying 5 cycles of SiO₂ coating further decreased the Pt concentration in the electrolyte to 1.9 mg L⁻¹. Nevertheless, continuing to increase the ALD coating to 20 cycles only caused a minor decrease in Pt concentration and did not significantly enhance the protection effect. This might be due to the crack formation on the relatively thick coating during the ADT process decreasing its protection ability.³⁶ This process can take place since the flexibility of SiO₂ decreases as the thickness increases and it has very low coefficient of expansion.³⁷ This implies that simply increasing ALD cycles to further reduce the Pt detachment after ADT is very challenging. The electrochemical oxidation potential of Pt is above 1.2 V vs. RHE.³⁸ Hence, Pt leaching during the ADT process should be negligible. The main mechanism for the Pt concentration increase after the ADT process should therefore be Pt detachment from the Pt/CB catalyst or catalyst peel off from the electrode. Overall, we show that the ultrathin SiO₂ layers deposited via ALD can be used to strongly reduce the Pt catalyst agglomeration and detachment during water splitting reaction.

Fig. 6 Particle size distribution of the Pt/CB catalyst before and after ADT: (a) original catalyst, Pt/CB catalyst coated with SiO₂ using (b) 5 ALD cycles, (c) 20 ALD cycles.

Table 1 Pt concentration in the electrolyte after ADT, tested by ICP-OES

Sample	Pt concentration (mg L^−1)
Fresh 0.5 M H2SO4 electrolyte	<0,02
Pt/CB without ALD coating	8.94
Pt/CB with 2 cycles coating	4.11
Pt/CB with 5 cycles coating	1.94
Pt/CB with 20 cycles coating	1.48

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Conclusions

ALD was employed to coat the surface of Pt/CB electrocatalysts with an ultrathin layer of SiO₂ to prevent deactivation during water electrolysis. Our findings show that without SiO₂ coating, the current density of the untreated Pt/CB catalyst was reduced by 34% at −0.2 V vs. RHE after an ADT. However, after coating the Pt/CB catalyst with 2 SiO₂ ALD cycles, the current density was only reduced by 7% under the same conditions. With 5 SiO₂ ALD cycles, the current density decrease was 2%. The Pt particle size increased by 16% after ADT without SiO₂ coating, but only by 3% after being protected by 5 cycles of SiO₂ deposition. Additionally, we observed severe Pt detachment after the ADT in the Pt/CB catalyst without ALD coating, with the Pt concentration in the electrolyte increasing to 8.9 mg L⁻¹ after ADT. The Pt detachment can be alleviated by the ultrathin SiO₂ coating synthesized by ALD. After applying 5 cycles of SiO₂ ALD, the Pt detachment/dissolution was reduced to one-fifth compared to the sample without ALD coating. In summary, a nanoscale SiO₂ protective layer strongly reduces Pt agglomeration and detachment during the hydrogen evolution reaction in acidic conditions. By performing just a few ALD cycles, keeping this coating ultrathin, an inhibitory effect on the electrocatalytic activity is avoided.

Author contributions

M. Li: conceptualization, methodology, formal analysis, validation, writing – original draft. S. Saedy: conceptualization, formal analysis, visualization, writing – review & editing. S. Fu: methodology, resources, investigation, writing – review & editing. T. Stellema: data curation, methodology, formal analysis, validation, visualization. R. Kortlever: supervision, writing – review & editing, project administration J. R. van Ommen: supervision, writing – review & editing, funding acquisition.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

M. L. and S. F. acknowledge the PhD scholarship awarded by the China Scholarship Council (CSC). The authors thank Mojgan Talebi for the help in the lab, Bart Boshuizen for the XPS line scan and XPS area scan training, Ruud Hendrikx for the XRD testing and Baukje Terpstra for the ICP-OES analysis.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3cy00996c

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