B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Abstract: The hydrogen evolution reaction (HER) requires stable and effective platinum (Pt)-based electrocatalysts. Traditional Pt powdery electrocatalysts face problems of dispersion and dissolution during the electrode preparation process and HER process. This leads to poor durability under high current density, especially if aiming for future industrial applications. Thus, platinum-based self-standing electrocatalysts were developed in this thesis for efficient and durable HER. Furthermore, traditional platinum-based electrocatalysts have limitations in HER activity in neutral and alkaline medium due to sluggish water dissociation, limited diffusion of H⁺ and slow desorption of H*. Therefore, based on selected substrates, Pt nanocrystals were grown directly on substrate as self-standing electrocatalyst, exploring the tuning of electronic structure in both experimental and theoretical results. First, Pt nanocrystals in the form of "blackberries" on copper (Cu) foams with minimal loading served as a self-standing electrode and the synthesis was accomplished by an easy, low-temperature strategy. The interaction between Pt and Cu foam was studied, leading to materials with ultra-stability under high current density. Second, based on the interaction between Pt and Cu, phosphorus was introduced to modify the surface environment, further increasing the HER performance in neutral medium. Third, Ni₂P/CoP nanosheet was grown directly on nickel (Ni) foam, which was considered as an efficient self-standing electrocatalyst. The synergistic effect was explored between Ni₂P and CoP. Furthermore, the as-prepared electrocatalyst was applied to domestic wastewater for HER, widening the feasibility of HER in complicated electrolytes. Fourth, Pt nanocrystals were grown on the edge of the Ni₂P/CoP nanosheet, forming a unique heterostructure, as a self-standing electrocatalyst. The local electric field effect and electronic structure were both explored, illustrating the remarkable HER activity in alkaline medium. This thesis described the modification of Pt nanocrystals on selected substrates as self-standing electrocatalyst for efficient and stable HER process.
|
Apr 2023
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Jack E. N.
Swallow
,
Elizabeth S.
Jones
,
Ashley R.
Head
,
Joshua S.
Gibson
,
Roey
Ben David
,
Michael W.
Fraser
,
Matthijs A.
Van Spronsen
,
Shaojun
Xu
,
Georg
Held
,
Baran
Eren
,
Robert S
Weatherup
Diamond Proposal Number(s):
[25834]
Open Access
Abstract: The reactions of H2, CO2, and CO gas mixtures on the surface of Cu at 200 °C, relevant for industrial methanol synthesis, are investigated using a combination of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and atmospheric-pressure near edge X-ray absorption fine structure (AtmP-NEXAFS) spectroscopy bridging pressures from 0.1 mbar to 1 bar. We find that the order of gas dosing can critically affect the catalyst chemical state, with the Cu catalyst maintained in a metallic state when H2 is introduced prior to the addition of CO2. Only on increasing the CO2 partial pressure is CuO formation observed that coexists with metallic Cu. When only CO2 is present, the surface oxidizes to Cu2O and CuO, and the subsequent addition of H2 partially reduces the surface to Cu2O without recovering metallic Cu, consistent with a high kinetic barrier to H2 dissociation on Cu2O. The addition of CO to the gas mixture is found to play a key role in removing adsorbed oxygen that otherwise passivates the Cu surface, making metallic Cu surface sites available for CO2 activation and subsequent conversion to CH3OH. These findings are corroborated by mass spectrometry measurements, which show increased H2O formation when H2 is dosed before rather than after CO2. The importance of maintaining metallic Cu sites during the methanol synthesis reaction is thereby highlighted, with the inclusion of CO in the gas feed helping to achieve this even in the absence of ZnO as the catalyst support.
|
Mar 2023
|
|
B07-B-Versatile Soft X-ray beamline: High Throughput
E02-JEM ARM 300CF
|
Longxiang
Liu
,
Liqun
Kang
,
Arunabhiram
Chutia
,
Jianrui
Feng
,
Martyna
Michalska
,
Pilar
Ferrer
,
David
Grinter
,
Georg
Held
,
Yeshu
Tan
,
Fangjia
Zhao
,
Fei
Guo
,
David
Hopkinson
,
Christopher
Allen
,
Yanbei
Hou
,
Junwen
Gu
,
Ioannis
Papakonstantinou
,
Paul
Shearing
,
Dan
Brett
,
Ivan P.
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[29340, 32501, 30614, 29809, 32058]
Open Access
Abstract: The electrochemical synthesis of hydrogen peroxide (H2O2) via a two-electron (2e-) oxygen reduction reaction (ORR) process provides a promising alternative to replace the energy-intensive anthraquinone process. However, the development of efficient electrocatalysts is still facing lots of challenges like insufficient understanding of active sites. Herein, we develop a facile template-protected strategy to synthesize a highly active quinone-rich porous carbon catalyst (PCC) for H2O2 electrochemical production. The optimized PCC900 exhibits unprecedented activity and selectivity, of which the onset potential reaches 0.83 V vs. reversible hydrogen electrode in 0.1 M KOH and the H2O2 selectivity is over 95 % in a wide potential range. Comprehensive synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with electrocatalytic characterizations reveals the positive correlation between quinone content and 2e- ORR performance. The effectiveness of chair-form quinone groups as the most efficient active sites is highlighted by the molecule-mimic strategy and theoretical analysis.
|
Mar 2023
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Diamond Proposal Number(s):
[22687]
Abstract: Designing CO2 methanation catalysts that meet industrial requirements is still challenging. We report Ni-Fe hydrotalcite-derived catalysts with a wide range of Ni and Mg loadings showing that an optimised composition with Ni0.4 gives a very high CO2 conversion rate of 0.37 mmol/gcat/s at 300°C. This catalyst is studied by in-situ APXPS and NEXAFS spectroscopies and compared with the other synthesised samples to obtain new mechanistic insights on methanation catalysts active for low-temperature (300°C) methanation, which is an industrial requirement. Under methanation conditions, in-situ investigations revealed the presence of metallic Ni sites and low nuclearity Ni-Fe species at
(Ni loading) = 21.2 mol%. These sites are oxidised on the low Ni-loaded catalyst (
= 9.2 mol%). The best CO2 conversion rate and CH4 selectivity are shown at intermediate
(21.2 mol%), in the presence of Mg. These superior performances are related to the high metallic surface area, dispersion, and optimal density of basic sites. The
(turnover frequency of CO2 conversion) increases exponentially with the fractional density of basic to metallic sites (
) from 1.1 s-1 (
= 29.2 mol%) to 9.1 s-1 (
= 7.6 mol%). It follows the opposite trend of the CO2 conversion rate. In-situ DRIFTS data under methanation conditions evidence that the
at high
is related to the presence of a formate route which is not predominant at low
(high
). A synergistic interplay of basic and metallic sites is present. This contribution provides a rationale for designing industrially competitive CO2 methanation catalysts with high catalytic activity while maintaining low Ni loading.
|
Mar 2023
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Elan D. R.
Mistry
,
Daphné
Lubert-Perquel
,
Irena
Nevjestic
,
Giuseppe
Mallia
,
Pilar
Ferrer
,
Kanak
Roy
,
Georg
Held
,
Tian
Tian
,
Nicholas M.
Harrison
,
Sandrine
Heutz
,
Camille
Petit
Diamond Proposal Number(s):
[26511]
Open Access
Abstract: A family of boron nitride (BN)-based photocatalysts for solar fuel syntheses have recently emerged. Studies have shown that oxygen doping, leading to boron oxynitride (BNO), can extend light absorption to the visible range. However, the fundamental question surrounding the origin of enhanced light harvesting and the role of specific chemical states of oxygen in BNO photochemistry remains unanswered. Here, using an integrated experimental and first-principles-based computational approach, we demonstrate that paramagnetic isolated OB3 states are paramount to inducing prominent red-shifted light absorption. Conversely, we highlight the diamagnetic nature of O–B–O states, which are shown to cause undesired larger band gaps and impaired photochemistry. This study elucidates the importance of paramagnetism in BNO semiconductors and provides fundamental insight into its photophysics. The work herein paves the way for tailoring of its optoelectronic and photochemical properties for solar fuel synthesis.
|
Feb 2023
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
Diamond Proposal Number(s):
[26226]
Open Access
Abstract: Batteries with inorganic solid-state electrolytes (ISSE) are attracting notable interest for next-generation systems implementing Lithium (Li) metal anodes, in view of achieving higher energy densities combined with superior safety. Notwithstanding extensive research and development work, this technology is not yet ready for industrial implementation, one of the key challenges being the stability of ISSEs, chiefly at the anodic interface. This work attacks this issue for the specific case of the LAGP/Li (Lithium Aluminium Germanium Phosphate/Lithium) interface with a micro-spectroscopic approach centred on post mortem Scanning Transmission X-ray Microscopy (STXM) of intact LMO/LAGP/Li thin-film batteries, microfabricated in discharged state. Pristine and cycled cells were mapped to pinpoint morphochemical changes, induced by electrochemical ageing. The evidenced shape changes, corresponding to mechanical damaging of the solid/solid electrodic interfaces correlate with LAGP decomposition at the anode, leading to reduction of Ge, whereas the chemical state at the cathodic interface is preserved. Thanks to its submicron spacial resolution, the STXM at the Ge L-edge and O K-edge spectra allowed to assess the highly localized nature of the chemical transformation of LAGP and its correlation with the formation of Li outgrowth features.
|
Nov 2022
|
|
B07-B-Versatile Soft X-ray beamline: High Throughput
B18-Core EXAFS
|
Jichao
Zhang
,
Xuedan
Song
,
Liqun
Kang
,
Jiexin
Zhu
,
Longxiang
Liu
,
Qing
Zhang
,
Dan J. I.
Brett
,
Paul R.
Shearing
,
Liqiang
Mai
,
Ivan P.
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[29340, 29271]
Open Access
Abstract: Layered hydroxides have shown superior catalytic activity for the electrocatalytic organic compound oxidation reaction. However, metal leaching can lead to uncontrollable structural phase transformation. Here, we report a Cr-Ni(OH)2 electrocatalyst as a model of a pre-catalyst for the identification of the structure-performance relationship. The optimized electrocatalyst delivered superb performances, i.e., a low potential of 1.38 V (versus reversible hydrogen electrode [RHE]) to reach 100 mA cm−2 and stable activity over 200 h at 10 mA cm−2. In situ analyses and theoretical calculations demonstrate that well-tuned electronic structures and the superhydrophilic-superaerophobic surface can enable rapid urea oxidation reaction (UOR) kinetics, which reduces the specific adsorption OH− and significantly depresses Cr dopants leaching, and this helps to maintain high UOR performance. Furthermore, the crucial role of mass transfer improvement to alleviate the structural decay under high potentials is disclosed.
|
Oct 2022
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Diamond Proposal Number(s):
[27982]
Abstract: Graphite is an integral part of lithium-ion batteries (LIBs). However, due to limited resources and high production cost of the highly purified (battery grade) graphite are becoming a challenge to meet the ever-increasing demands for energy storage devices. One viable approach is to recycle the spent graphite anodes from end-of-life LIBs. Importantly, recycling of spent lithium-ion batteries (LIBs) is off utmost importance to address the global challenge of electronic waste management. Herein, we present an environment friendly technique of graphite recycling from the spent LIB by water leaching, followed by atmospheric plasma jet printing. The major advantage of this method is that it does not require any binders or conductive diluents. Plasma printed recycled graphite showed significantly enhanced specific capacity of 402 mAh g−1 at 500 mA g−1 at the end of the 1000th charge-discharge cycles, in comparison to with water-washed recycled graphite (112 mAh g−1) and a 23.35 times faster diffusivity of Li+. A detailed experimental investigation revealed the plasma activation of the graphitic structure resulted in the improved reversible Li+ storage. This work provides a new perspective on the recycling strategy of graphite anodes using the in-situ plasma functionalization strategy, a significant step towards the sustainable future of LIBs.
|
Jul 2022
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
Diamond Proposal Number(s):
[23049]
Open Access
Abstract: The persistence of organic carbon (OC) in natural environments is widely attributed to mineral protection, especially by iron (Fe) (oxyhydr)oxides. The effect of OC binding strength on the aging of Fe (oxyhydr)oxides and the mobility and fate of OC during aging however, is unknown. Here we investigate how OC binding strength controls the aging of ferrihydrite (Fh) and subsequent retention or release of the associated OC. We focus on carboxyl-rich OC coprecipitated with Fh and track the physiochemical properties and OC stability as a function of carboxyl-richness over time. In agreement with previous work we find that during carboxyl-rich OC coprecipitation with Fh, OC is adsorbed to the Fh particle surfaces and that increasing carboxyl-richness results in an increasing number of carboxylate-Fe bonds between the OC and the mineral particles and thus increasing OC binding strength. We show that OC substantially retards the aging of Fe (oxyhydr)oxide from Fh to more crystalline Fe minerals and that this retardation increases with increasing OC binding strength. We also show that the total amount of OC decreases during aging and that the proportion of the remaining OC that is non-desorbable with 0.1 M NaOH decreases during aging for OC with relatively low binding strength but increases during aging for OC with relatively high binding strength. Our results therefore indicate that OC with higher binding strength coprecipitated with Fh becomes proportionally more stable with the solid phase and thus less mobile during aging in natural environments. We suggest that our work might offer a deeper mechanistic insight into the processes responsible for OC persistence with minerals and thus the long-term preservation of OC in natural environments.
|
Jul 2022
|
|
I08-Scanning X-ray Microscopy beamline (SXM)
|
Diamond Proposal Number(s):
[20567]
Abstract: To assess the safety of engineered nanomaterials (ENMs) and to evaluate and improve ENMs’ targeting ability for medical application, it is necessary to analyze the fate of these materials in biological media. This protocol presents a workflow that allows researchers to determine, characterize and quantify metal-bearing ENMs (M-ENMs) in biological tissues and cells and quantify their dynamic behavior at trace-level concentrations. Sample preparation methods to enable analysis of M-ENMs in a single cell, a cell layer, tissue, organ and physiological media (e.g., blood, gut content, hemolymph) of different (micro)organisms, e.g., bacteria, animals and plants are presented. The samples are then evaluated using fit-for-purpose analytical techniques e.g., single-cell inductively coupled plasma mass spectrometry, single-particle inductively coupled plasma mass spectrometry and synchrotron X-ray absorption fine structure, providing a protocol that allows comprehensive characterization and quantification of M-ENMs in biological matrices. Unlike previous methods, the protocol uses no fluorescent dyes or radiolabels to trace M-ENMs in biota and enables analysis of most M-ENMs at cellular, tissue and organism levels. The protocols can be applied by a wide variety of users depending on the intended purpose of the application, e.g., to correlate toxicity with a specific particle form, or to understand the absorption, distribution and excretion of M-ENMs. The results facilitate an understanding of the biological fate of M-ENMs and their dynamic behavior in biota. Performing the protocol may take 7–30 d, depending on which combination of methods is applied.
|
Jun 2022
|
|
