راه حل های بهتر برای ساخت هیدروژن ممکن است فقط در سطح باشد

بازنشر افلاطون

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صفحه اصلی > رسانه ها و مطبوعات راه حل های بهتر برای ساخت هیدروژن ممکن است فقط در سطح قرار داشته باشند

فعل و انفعالات منحصر به فرد بین اکسید پروسکایت، لایه سطحی در حال تغییر آن و گونه های آهنی که در جهت OER فعال هستند، مسیر جدیدی را برای طراحی مواد فعال و پایدار هموار می کند و ما را یک قدم به تولید هیدروژن سبز کارآمد و مقرون به صرفه نزدیک می کند. CREDIT آزمایشگاه ملی آرگون

چکیده:
A clean energy future propelled by hydrogen fuel depends on figuring out how to reliably and efficiently split water. That’s because, even though hydrogen is abundant, it must be derived from another substance that contains it — and today, that substance is often methane gas. Scientists are seeking ways to isolate this energy-carrying element without using fossil fuels. That would pave the way for hydrogen-fueled cars, for example, that emit only water and warm air at the tailpipe.

راه حل های بهتر برای ساخت هیدروژن ممکن است فقط در سطح باشد

Argonne، IL | ارسال شده در 9 آوریل 2021

Water, or H2O, unites hydrogen and oxygen. Hydrogen atoms in the form of molecular hydrogen must be separated out from this compound. That process depends on a key — but often slow — step: the oxygen evolution reaction (OER). The OER is what frees up molecular oxygen from water, and controlling this reaction is important not only to hydrogen production but a variety of chemical processes, including ones found in batteries.

“The oxygen evolution reaction is a part of so many processes, so the applicability here is quite broad.” — Pietro Papa Lopes, Argonne assistant scientist

A study led by scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory illuminates a shape-shifting quality in perovskite oxides, a promising type of material for speeding up the OER. Perovskite oxides encompass a range of compounds that all have a similar crystalline structure. They typically contain an alkaline earth metal or lanthanides such as La and Sr in the A-site, and a transition metal such as Co in the B-site, combined with oxygen in the formula ABO3. The research lends insight that could be used to design new materials not only for making renewable fuels but also storing energy.

اکسیدهای پروسکایت می توانند OER را ایجاد کنند و نسبت به فلزات گرانبها مانند ایریدیوم یا روتنیم که این کار را نیز انجام می دهند، ارزان تر هستند. اما اکسیدهای پروسکایت به اندازه این فلزات فعال (به عبارت دیگر، در تسریع OER کارآمد) نیستند و به آرامی تجزیه می شوند.

“Understanding how these materials can be active and stable was a big driving force for us,” said Pietro Papa Lopes, an assistant scientist in Argonne’s Materials Science division who led the study. “We wanted to explore the relationship between these two properties and how that connects to the properties of the perovskite itself.”

تحقیقات قبلی بر روی خواص عمده مواد پروسکایت و نحوه ارتباط آنها با فعالیت OER متمرکز شده است. با این حال، محققان متعجب بودند که آیا این داستان چیز بیشتری دارد یا خیر. از این گذشته، سطح یک ماده، جایی که با محیط اطراف خود واکنش نشان می دهد، می تواند کاملاً متفاوت از بقیه باشد. نمونه هایی از این دست در همه جا در طبیعت وجود دارد: آووکادویی نصف شده را در نظر بگیرید که در جایی که با هوا برخورد می کند به سرعت قهوه ای می شود اما داخل آن سبز باقی می ماند. برای مواد پروسکایتی، سطحی که با توده متفاوت می شود، می تواند پیامدهای مهمی برای درک ما از خواص آنها داشته باشد.

In water electrolyzer systems, which split water into hydrogen and oxygen, perovskite oxides interact with an electrolyte made of water and special salt species, creating an interface that allows the device to operate. As electrical current is applied, that interface is critical in kicking off the water-splitting process. “The material’s surface is the most important aspect of how the oxygen evolution reaction will proceed: How much voltage you need, and how much oxygen and hydrogen you’re going to be producing,” Lopes said.

Not only is the perovskite oxide’s surface different from the rest of the material, it also changes over time. “Once it’s in an electrochemical system, the perovskite surface evolves and turns into a thin, amorphous film,” Lopes said. “It’s never really the same as the material you start with.”

The researchers combined theoretical calculations and experiments to determine how the surface of a perovskite material evolves during the OER. To do so with precision, they studied lanthanum cobalt oxide perovskite and tuned it by “doping” the lanthanum with strontium, a more reactive metal. The more strontium was added to the initial material, the faster its surface evolved and became active for the OER — a process the researchers were able to observe at atomic resolution with transmission electron microscopy. The researchers found that strontium dissolution and oxygen loss from the perovskite were driving the formation of this amorphous surface layer, which was further explained by computational modelling performed using the Center for Nanoscale Materials, a DOE Office of Science User Facility.

“The last missing piece to understand why the perovskites were active towards the OER was to explore the role of small amounts of iron present in the electrolyte,” Lopes said. The same group of researchers recently discovered that traces of iron can improve the OER on other amorphous oxide surfaces. Once they determined that a perovskite surface evolves into an amorphous oxide, then it became clear why iron was so important.

“Computational studies help scientists understand reaction mechanisms that involve both the perovskite surface and the electrolyte,” said Peter Zapol, a physicist at Argonne and study co-author. “We focused on reaction mechanisms that drive both activity and stability trends in perovskite materials. This is not typically done in computational studies, which tend to focus solely on the reaction mechanisms responsible for the activity.”

The study found that the perovskite oxide’s surface evolved into a cobalt-rich amorphous film just a few nanometers thick. When iron was present in the electrolyte, the iron helped accelerate the OER, while the cobalt-rich film had a stabilizing effect on the iron, keeping it active at the surface.

The results suggest new potential strategies for designing perovskite materials — one can imagine creating a two-layer system, Lopes said, that is even more stable and capable of promoting the OER.

“The OER is a part of so many processes, so the applicability here is quite broad,” Lopes said. “Understanding the dynamics of materials and their effect on the surface processes is how we can make energy conversion and storage systems better, more efficient and affordable.”

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The study is described in a paper published and highlighted on the Feb. 24 cover of the Journal of the American Chemical Society, “Dynamically Stable Active Sites from Surface Evolution of Perovskite Materials during the Oxygen Evolution.” In addition to Lopes and Zapol, coauthors include Dong Young Chung, Hong Zheng, Pedro Farinazzo Bergamo Dias Martins, Dusan Strmcnik, Vojislav Stamenkovic, Nenad Markovic and John Mitchell at Argonne; Xue Rui and Robert Klie at the University of Illinois at Chicago; and Haiying He at Valparaiso University. This research was funded by DOE’s Office of Basic Energy Sciences.

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درباره آزمایشگاه ملی آرگون
آزمایشگاه ملی آرگون به دنبال راه حلی برای مشکلات ملی در علم و فناوری است. اولین آزمایشگاه ملی کشور، Argonne، تحقیقات علمی پایه و کاربردی پیشرو را تقریباً در هر رشته علمی انجام می دهد. محققان Argonne از نزدیک با محققین صدها شرکت، دانشگاه، و سازمان های فدرال، ایالتی و شهرداری همکاری می کنند تا به آنها کمک کنند تا مشکلات خاص خود را حل کنند، رهبری علمی آمریکا را پیش ببرند و کشور را برای آینده ای بهتر آماده کنند. با کارکنان بیش از 60 کشور، Argonne توسط UChicago Argonne، LLC برای دفتر علوم وزارت انرژی ایالات متحده مدیریت می شود.

درباره مرکز مواد نانومقیاس Argonne

The Center for Nanoscale Materials is one of the five DOE Nanoscale Science Research Centers, premier national user facilities for interdisciplinary research at the nanoscale supported by the DOE Office of Science. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia and Los Alamos National Laboratories. For more information about the DOE NSRCs, please visit https://science.osti.gov/User-Facilities/User-Facilities-at-a-Glance.

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