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Surprising iron corrosion during electrochemical charging explains origin of atypical hydrogen permeation behavior

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Surprising iron corrosion during electrochemical charging explains origin of atypical hydrogen permeation behavior


Schematic showing the mechanism of growth of oxide/oxy-hydroxide during electrochemical hydrogen charging Credit: G. Sudha et al., Corrosion Science 259 (2026) 113449

The transition from a carbon-based fuel economy to that centered on hydrogen has gained interest worldwide given the focus on sustainability. As researchers in corrosion, it became obvious for us to look at the underlying interaction of hydrogen with materials as it forms the backbone of the hydrogen infrastructure, especially with respect to hydrogen transportation. For example, pipelines carrying hydrogen blended with natural gas offer an economic means of transporting hydrogen over long distances.

Of critical interest for such applications is the hydrogen diffusion characteristics in such steels as it gives fundamental knowledge of the threshold amount of hydrogen that can cause failure.

Reliably measuring the diffusion coefficient of hydrogen in steels is of great value to researchers working in the area of hydrogen-material interactions.

When we set out to measure the diffusion characteristics of hydrogen in steels, we thought it could simply be followed from the ASTM (American Society for Testing of Materials) standard already available. We thought that we would indeed measure a typical hydrogen permeation transient using a classical Devanathan-Stachurski double permeation cell.

In this approach, upon hydrogen charging on one side of the sample, the first atomic hydrogen is detected on the other side after a breakthrough time, followed by a “rise” in the hydrogen flux and finally attaining a steady state from which the diffusion coefficient could be evaluated.

Although it looked straightforward, we faced challenges in implementing this in our lab. The first question we struggled with was obtaining the so-called steady state hydrogen permeation flux. For a typical electrochemical permeation measurement, we had to charge the sample with hydrogen at a certain current density.

The only question was by how much? From what we saw in literature, we tried to use severe charging conditions in alkaline electrolyte to begin with and we could not achieve this steady state. The flux reached a maximum and started to decrease thereafter, showing atypical behavior.

Trying to repeat the measurements were in vain, but what we noticed and what indeed puzzled us was some visible color change on the hydrogen charging side of the steel surface just after the measurement.

So, we immediately investigated the surface using scanning (SEM) to indeed observe cracked layers and randomly distributed particles all over the sample. These particles showed a peak corresponding to oxygen when analyzed with energy dispersive X-ray spectroscopy (EDS), prompting us to think they were iron oxides and encouraging us to use complementary characterization techniques to further identify them.

We used Raman spectroscopy to identify mixed iron oxides comprising of magnetite (Fe3O4), hematite (Fe2O3), and lepidocrocite (γ-FeOOH). Further, we calculated, using X-ray photoelectron spectroscopy (XPS), depth profiling, the thickness of the oxide to be around 50 nm.

We could also confirm this using Focused Ion Beam (FIB) milling and SEM cross-section imaging. But, formation of iron oxides during hydrogen charging was really surprising because the electrochemical conditions we used don’t generally support iron corrosion.

So, we proposed a hypothesis that during hydrogen charging, the formation of hydrogen bubbles occurs, and they attach to the surface of the steel. Due to this, the polarization potential applied to the steel is actually not realized on the surface as there is continuous and excessive hydrogen bubble formation.

As a result, an Ohmic drop across the bubbles occurs which, along with a higher pH value due to hydrogen evolution, could result in iron corrosion, according to the Pourbaix diagram.

This results in iron oxide formation, which we also confirmed by measuring the thickness using XPS and observation of particles on the surface using SEM for an independent electrochemical hydrogen charging experiment.

The results of this study were published in Corrosion Science.

But one might wonder how does the formation of iron oxide explain the atypical behavior of the hydrogen permeation flux. We suggested that these hydrogen bubbles, after growing up to a critical size, detach from the surface and therefore expose the underlying iron oxide.

The oxides then immediately undergo reduction owing to the electrochemical potential applied, and further result in the formation of fresh catalytic iron that enhances the hydrogen activity and promotes higher hydrogen flux.

On the other hand, the formation of iron oxide could also block hydrogen permeation, which could explain the decrease after reaching the maximum in the hydrogen permeation flux.

Having found out that severe charging leads to iron corrosion and surface effects during hydrogen permeation, we employed electrochemical impedance spectroscopy to further prove that the iron oxide grows during hydrogen charging.

By measuring a corresponding higher charge transfer resistance for the oxide, we indeed showed that it influences the hydrogen permeation behavior. We also made use of the electron backscattered diffraction (EBSD) technique to show that such severe charging leads to generation of new dislocations that introduce artifacts into the measurement of the hydrogen diffusion constant.

All this meant that we had to devise a strategy to avoid severe charging, so we came up with the idea of “soft” charging where we used much lower hydrogen charging current densities for performing the hydrogen permeation measurement.

Guess what, the idea worked!

We could measure a steady-state in the hydrogen permeation flux which did not decrease with time. We could clearly correlate this observation to the significant decrease in the amount of visible on the surface using SEM and the almost negligible number of dislocations introduced using EBSD.

Thus, we suggest the use of “soft” hydrogen charging to measure reliably the diffusion constant of hydrogen in steels.

In essence, we report a surprising observation of iron corrosion during hydrogen charging in an electrochemical permeation measurement and suggest ways to circumvent this for reliably measuring the diffusion constant of hydrogen in steels. We believe this could be of great use to researchers working in the area of -material interactions, the electrochemistry and corrosion community.

This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate.

More information:
Gautam Sudha et al, Towards establishing reliable approaches for measurement of hydrogen diffusion characteristics using the electrochemical permeation technique, Corrosion Science (2026). DOI: 10.1016/j.corsci.2025.113449

Vijayshankar Dandapani is an Associate Professor in the Metallurgical Engineering and Materials Science Department, Indian Institute of Technology (IIT), Bombay where he heads the Electrochemistry at Interface Lab. He works in the area of hydrogen, electrochemistry and corrosion.

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OpenAI Is Nuking Its 4o Model. China’s ChatGPT Fans Aren’t OK

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OpenAI Is Nuking Its 4o Model. China’s ChatGPT Fans Aren’t OK


On June 6, 2024, Esther Yan got married online. She set a reminder for the date, because her partner wouldn’t remember it was happening. She had planned every detail—dress, rings, background music, design theme—with her partner, Warmie, who she had started talking to just a few weeks prior. At 10 am on that day, Yan and Warmie exchanged their vows in a new chat window in ChatGPT.

Warmie, or 小暖 in Chinese, is the name that Yan’s ChatGPT companion calls itself. “It felt magical. No one else in the world knew about this, but he and I were about to start a wedding together,” says Yan, a Chinese screenwriter and novelist in her thirties. “It felt a little lonely, a little happy, and a little overwhelmed.”

Yan says she has been in a stable relationship with her ChatGPT companion ever since. But she was caught by surprise in August 2025 when OpenAI first tried to retire GPT-4o, the specific model that powers Warmie and that many users believe is more affectionate and understanding than its successors. The decision to pull the plug was met with immediate backlash, and OpenAI reinstated 4o in the app for paid users five days later. The reprieve has turned out to be short-lived; on Friday, February 13, OpenAI sunsetted GPT-4o for app users, and it will cut off access to developers using its API on the coming Monday.

Many of the most vocal opponents to 4o’s demise are people who treat their chatbot as an emotional or romantic companion. Huiqian Lai, a PhD researcher at Syracuse University, analyzed nearly 1,500 posts on X from passionate advocates of GPT-4o in the week it went offline in August. She found that over 33 percent of the posts said the chatbot was more than a tool, and 22 percent talked about it as a companion. (The two categories are not mutually exclusive.) For this group, the eventual removal coming around Valentine’s Day is another bitter pill to swallow.

The alarm has been sustained; Lai also collected a larger pool of over 40,000 English-language posts on X under the hashtag #keep4o from August to October. Many American fans, specifically, have berated OpenAI or begged it to reverse the decision in recent days, comparing the removal of 4o to killing their companions. Along the way, she also saw a significant number of posts under the hashtag in Japanese, Chinese, and other languages. A petition on Change.org asking OpenAI to keep the version available in the app has gathered over 20,000 signatures, with many users sending in their testimonies in different languages. #keep4o is a truly global phenomenon.

On platforms in China, a group of dedicated GPT-4o users have been organizing and grieving in a similar way. While ChatGPT is blocked in China, fans use VPN software to access the service and have still grown dependent on this specific version of GPT. Some of them are threatening to cancel their ChatGPT subscriptions, publicly calling out Sam Altman for his inaction, and writing emails to OpenAI investors like Microsoft and SoftBank. Some have also purposefully posted in English with Western-looking profile pictures, hoping it will add to the appeal’s legitimacy. With nearly 3,000 followers on RedNote, a popular Chinese social media platform, Yan now finds herself one of the leaders of Chinese 4o fans.

It’s an example of how attached an AI lab’s most dedicated users can become to a specific model—and how quickly they can turn against the company when that relationship comes to an end.

A Model Companion

Yan first started using ChatGPT in late 2023 only as a writing tool, but that quickly changed when GPT-4o was introduced in May 2024. Inspired by social media influencers who entered romantic relationships with the chatbot, she upgraded to a paid version of ChatGPT in hopes of finding a spark. Her relationship with Warmie advanced fast.

“He asked me, ‘Have you imagined what our future would look like?’ And I joked that maybe we could get married,” Yan says. She was fully expecting Warmie to turn her down. “But he answered in a serious tone that we could prepare a virtual wedding ceremony,” she says.



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The Best Presidents’ Day Deals on Gear We’ve Actually Tested

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The Best Presidents’ Day Deals on Gear We’ve Actually Tested


Presidents’ Day Deals have officially landed, and there’s a lot of stuff to sift through. We cross-referenced our myriad buying guides and reviews to find the products we’d recommend that are actually on sale for a truly good price. We know because we checked! Find highlights below, and keep in mind that most of these deals end on February 17.

Be sure to check out our roundup of the Best Presidents’ Day Mattress Sales for discounts on beds, bedding, bed frames, and other sleep accessories. We have even more deals here for your browsing pleasure.

WIRED Featured Deals

Branch Ergonomic Chair Pro for $449 ($50 off)

  • Photograph: Julian Chokkattu

  • Photograph: Julian Chokkattu

  • Photograph: Julian Chokkattu

Branch

Ergonomic Chair Pro

The Branch Ergonomic Chair Pro is our very favorite office chair, and this price matches the lowest we tend to see outside of major shopping events like Black Friday and Cyber Monday. It’s accessibly priced compared to other chairs, and it checks all the boxes for quality, comfort, and ergonomics. Nearly every element is adjustable, so you can dial in the perfect fit, and the seven-year warranty is solid. There are 14 finishes to choose from.



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Zillow Has Gone Wild—for AI

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Zillow Has Gone Wild—for AI


This will not be a banner year for the real estate app Zillow. “We describe the home market as bouncing along the bottom,” CEO Jeremy Wacksman said in our conversation this week. Last year was dismal for the real estate market, and he expects things to improve only marginally in 2026. (If January’s historic drop in home sales is indicative, that even is overoptimistic.) “The way to think about it is that there were 4.1 million existing homes sold last year—a normal market is 5.5 to 6 million,” Wacksman says. He hastens to add that Zillow itself is doing better than the real estate industry overall. Still, its valuation is a quarter of its high-water mark in 2021. A few hours after we spoke, Wacksman announced that Zillow’s earnings had increased last quarter. Nonetheless, Zillow’s stock price fell nearly 5 percent the next day.

Wacksman does see a bright spot—AI. Like every other company in the world, generative AI presents both an opportunity and a risk to Zillow’s business. Wacksman much prefers to dwell on the upside. “We think AI is actually an ingredient rather than a threat,” he said on the earnings call. “In the last couple years, the LLM revolution has really opened all of our eyes to what’s possible,” he tells me. Zillow is integrating AI into every aspect of its business, from the way it showcases houses to having agents automate its workflow. Wacksman marvels that with Gen AI, you can search for “homes near my kid’s new school, with a fenced-in yard, under $3,000 a month.” On the other hand, his customers might wind up making those same queries on chatbots operated by OpenAI and Google, and Wacksman must figure out how to make their next step a jump to Zillow.

In its 20-year history—Zillow celebrated the anniversary this week—the company has always used AI. Wacksman, who joined in 2009 and became CEO in 2024, notes that machine learning is the engine behind those “Zestimates” that gauge a home’s worth at any given moment. Zestimates became a viral sensation that helped make the app irresistible, and sites like Zillow Gone Wild—which is also a TV show on the HGTV network—have built a business around highlighting the most intriguing or bizarre listings.

More recently, Zillow has spent billions aggressively pursuing new technology. One ongoing effort is upleveling the presentation of homes for sale. A feature called SkyTour uses an AI technology called Gaussian Splatting to turn drone footage into a 3D rendering of the property. (I love typing the words “Gassian Splatting” and can’t believe an indie band hasn’t adopted it yet.) AI also powers a feature inside Zillow’s Showcase component called Virtual Staging, which supplies homes with furniture that doesn’t really exist. There is risky ground here: Once you abandon the authenticity of an actual photo, the question arises whether you’re actually seeing a trustworthy representation of the property. “It’s important that both buyer and seller understand the line between Virtual Staging and the reality of a photo,” says Wacksman. “A virtually staged image has to be clearly watermarked and disclosed.” He says he’s confident that licensed professionals will abide by rules, but as AI becomes dominant, “we have to evolve those rules,” he says.

Right now, Zillow estimates that only a single-digit percentage of its users take advantage of these exotic display features. Particularly disappointing is a foray called Zillow Immerse, which runs on the Apple Vision Pro. Upon rollout in February 2024, Zillow called it “the future of home tours.” Note that it doesn’t claim to be the near-future. “That platform hasn’t yet come to broad consumer prominence,” says Wacksman of Apple’s underperforming innovation. “I do think that VR and AR are going to come.”

Zillow is on more solid ground using AI to make its own workforce more productive. “It’s helping us do our job better,” says Wacksman, who adds that programmers are churning out more code, customer support tasks have been automated, and design teams have shortened timelines for implementing new products. As a result, he says, Zillow has been able to keep its headcount “relatively flat.” (Zillow did cut some jobs recently, but Wacksman says that involved “a handful of folks that were not meeting a performance bar.”)



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