Tag: Spectromicroscopy

Metallic nanocatalysts: what really happens during catalysis

Metallic nanocatalysts: what really happens during catalysis

Using a combination of spectromicroscopy at BESSY II and microscopic analyses at DESY’s NanoLab, a team has gained new insights into the chemical behaviour of nanocatalysts during catalysis. The nanoparticles consisted of a platinum core with a rhodium shell. This configuration allows a better understanding of structural changes in, for example, rhodium-platinum catalysts for emission control. The results show that under typical catalytic conditions, some of the rhodium in the shell can diffuse into the interior of the nanoparticles. However, most of it remains on the surface and oxidises. This process is strongly dependent on the surface orientation of the nanoparticle facets.

Nanoparticles measure less than one ten-thousandth of a millimetre in diameter and have enormous surface areas in relation to their mass. This makes them attractive as catalysts: metallic nanoparticles can facilitate chemical conversions, whether for environmental protection, industrial synthesis or the production of (sustainable) fuels from CO2 and hydrogen.

Platinum core with Rhodium shell

Platinum (Pt) is one of the best-known metal catalysts and is used in heterogeneous gas phase catalysis for emission control, for example to convert toxic carbon monoxide in car exhaust gases from combustion engines into non-toxic CO2. ‘Mixing platinum particles with the element rhodium (Rh) can further increase efficiency,’ says Jagrati Dwivedi, first author of the publication. The location of the two elements plays an important role in this process. So-called core-shell nanoparticles with a platinum core and an extremely thin rhodium shell can help in the search for the optimal element distribution that can extend the lifetime of the nanoparticles.

Experiments at BESSY II and DESY NanoLab

Until now, however, little was known about how the chemical composition of a catalyst’s surface changes during operation. A team led by Dr Thomas F. Keller, head of the microscopy group at DESY NanoLab, has now investigated such crystalline Pt-Rh nanoparticles at BESSY II and gained new insights into the changes at the facets of the polyhedral nanoparticles.

The nanoparticles were first characterised and marked in their vicinity using scanning electron microscopy and atomic force microscopy at DESY NanoLab. These markers were then used to analyse the same nanoparticles spectroscopically and image them microscopically simultaneously using X-ray light on a special instrument at BESSY II.

The SMART instrument at the Fritz Haber Institute of the Max Planck Society enables X-ray photoemission electron microscopy (XPEEM) in a microscope mode. This makes it possible to distinguish individual elements with high spatial resolution, enabling the observation of chemical processes at near-surface atomic layers. ‘The instrument allows the chemical analysis of individual elements with a resolution of 5-10 nanometres, which is unique,’ says Thomas Keller. The investigation has shown that rhodium can partially diffuse into the platinum cores during catalysis: both elements are miscible at the typical operating temperatures of the catalyst. The mixing is enhanced in a reducing environment (H2) and slowed down in an oxidising environment (O2) without reversing the net flow of rhodium into platinum. ‘At higher temperatures, this process even increases significantly,’ explains Keller.

Read more on BESSY II website

MXenes for energy storage: Chemical imaging more than just surface deep

MXenes for energy storage: Chemical imaging more than just surface deep

A new method in spectromicroscopy significantly improves the study of chemical reactions at the nanoscale, both on surfaces and inside layered materials. Scanning X-ray microscopy (SXM) at MAXYMUS beamline of BESSY II enables the investigation of chemical species adsorbed on the top layer (surface) or intercalated within the MXene electrode (bulk) with high chemical sensitivity. The method was developed by a HZB team led by Dr. Tristan Petit. The scientists demonstrated among others first SXM on MXene flakes, a material used as electrode in lithium-ion batteries.

Since their discovery in 2011, MXenes have gathered significant scientific interest due to their versatile tunable properties and diverse applications, from energy storage to electromagnetic shielding. Researchers have been working to decipher the complex chemistry of MXenes at the nanoscale.

The team of Dr. Tristan Petit now made a significant progress in MXene characterization, as described in their recent publication. They utilized SXM to investigate the chemical bonding of Ti3C2Tx MXenes, with Tx denoting the terminations (Tx=O, OH, F, Cl), with high spatial and spectral resolution. The novelty in this work is to combine simultaneously two detection modes, transmission and electron yield, enabling different probing depths.

SXM provided detailed insights into the chemical composition and structure of MXenes. According to Faidra Amargianou, first author of the study: “Our findings shed light on the chemical bonding within MXene structure, and with surrounding species, offering new perspective for their utilization across various applications, especially in electrochemical energy storage.”

Read more on HZB website

Image: Scanning X-ray images of a dismounted Li-ion battery with cycled MXene electrode (green), electrolyte/ carbonate species (red) and separator (yellow). The Transmission (bulk-sensitive) image is on the left, the electron yield (surface-sensitive) image on the right.

Credit: HZB

Diamond helps find a way to improve accuracy of Lateral Flow Tests

Diamond helps find a way to improve accuracy of Lateral Flow Tests

A recent study has found a way to help reduce false-negative results in Lateral Flow Tests by a simple modification.

Using X-ray fluorescence imaging at Diamond, researchers from King’s College London set out to identify what could be causing these false-negative results, and what potential modifications could enable increased accuracy.

They identified that the underlying technology of the Lateral Flow Devices is highly accurate and able to theoretically detect trace amounts of the COVID-19 virus, but the limitations fall to the read-out of the device – the technology used to communicate the result of the test.

The study, published in ACS Materials and Interfaces, suggests  several potentially simple modifications to the Lateral Flow Devices that could lead to improved performance.

read more on the Diamond website

Preparing for the next generation of batteries

Preparing for the next generation of batteries

In the ongoing quest to build a better battery, researchers used the Canadian Light Source (CLS) at the University of Saskatchewan to identify the potential of using polymer composites as electrode matrices to increase the capacity of rechargeable lithium-ion (Li-ion) batteries.

“The composition of the adhesive and conductive framework for batteries hasn’t changed in years,” said Dr. Christian Kuss, assistant professor in the Department of Chemistry at the University of Manitoba and one of three researchers on the project. “But, we’re reaching the limit of how much capacity Li-Ion batteries have so this work is essentially preparing for the next generation of batteries.”

Over many cycles of charging and discharging, battery materials begin to break down, he explained. “The goal is to find new matrix materials that allow the electrode to stay intact over longer periods of time and thereby increase capacity.”

The new matrix material Kuss and his colleagues studied was based on a mixture of two polymers – one adhesive and the other conductive. The adhesive polymer is cellulose based, he said, while the conductive one “is easily synthesized and fairly cheap.” Cost is an important consideration “because you ultimately want a battery that is comparable in terms of pricing to what’s already available.”

At the CLS, the researchers used the Spectromicroscopy beamline to study the chemical structure of the polymer mixture. “With this technique, we could see the mixture and see how the polymers were distributed at a microscale.”

Read more on the CLS website

Image: Battery cyclers for running and testing batteries.