Liquid phase (scanning) transmission electron microscopy (LP-(S)TEM) enables exploring processes down to the nanoscale. This allows to unravel degradation pathways of electrocatalysts, such as silver nanostructures, which gained attention for CO2 upconversion. However, the nanoscale resolution in LP-TEM comes at the cost of introducing new effects such as radiolysis, and with the emergence of liquid cell systems with active mass transport, the impact of advection must be considered when evaluating the radiolytic on-site chemistry. We provide proof of a chemical environment control depending on systematically varied liquid flow velocity and dwell time at a constant dose rate. Using AgNO3 as a probe solution, our findings show a clear dependence of nanosilver evolution on these parameters, ranging from fast growth to dissolution. This implies a change between reductive and oxidative conditions, achieved by independently adjusting volumetric flow rate or dwell time. Kinetic modeling further supports the underlying radiation chemistry. Our results illustrate that a precise understanding of flow-mediated radiation chemistry is crucial in LP-TEM and paves the way for performing controlled operando studies into materials degradation without the electron probe being the driving force.

Paired electrolysis offers an auspicious strategy for the generation of high-value chemicals, at both the anode and cathode, in an integrated electrochemical reactor. Through efficient electron utilization, routine product misuse at overlooked electrodes can be prevented. Here, an original paired electrosynthetic system is reported that can convert CO2 to ethylene (C2H4) at the cathode, and water to hydrogen peroxide (H2O2) at the anode under a single pass of electric charge. Amongst various investigated copper (Cu) nanomorphologies, the bespoke mixed Cu nanowire/nanoparticle catalyst recorded a peak C2H4 Faraday efficiency (FE) of 60% following 370 h of electrolysis at 200 mA cm(-2), while the tailored boron-doped diamond (BDD) anode accumulated an unprecedented approximate to 1% w/w of H2O2 in 4 m K2CO3 upon applying 300 mA cm(-2) for 10 h. When paired, the dual C2H4-H2O2 electrochemical cell attains a combined FE of 120% for 50 h at 200 mA cm(-2), a combined energy efficiency (EE) of 69%, and a 50% decrease in the overall electrical energy consumption (EEC) compared to the individual electrosynthesis of C2H4 and H2O2.

Fundamental research campaigns in electrocatalysis often involve the use of model systems, such as single crystals or magnetron-sputtered thin films (single metals or metal alloys). The downsides of these approaches are that oftentimes only a limited number of compositions are picked and tested (guided by chemical intuition) and that the validity of trends is not verified under operating conditions typically present in real devices. These together can lead to deficient conclusions, hampering the direct application of newly discovered systems in real devices. In this contribution, the stability of magnetron-sputtered bimetallic PtxRuy thin film electrocatalysts (0 at. % to 100 at. % Ru content) along with three commercially available carbon-supported counterparts (50-67 at. % Ru content) was mapped under electrocatalytic conditions in acidic electrolytes using online ICP-MS. We found several differences between the two systems in the amount of metals dissolved along with the development of the morphology and composition. While the Pt-rich PtxRuy compositions remained unchanged, 30-50 nm diameter surface pits were detected in the case of the Ru-rich sputtered thin films. Contrastingly, the surface of the carbon-supported NPs enriched in Pt accompanied by the leaching of a significant amount of Ru from the alloy structure was observed. Change in morphology was accompanied by a mass loss reaching around 1-2 wt % in the case of the sputtered samples and almost 10 wt % for the NPs. Since PtxRuy has prime importance in driving alcohol oxidation reactions, the stability of all investigated alloys was screened in the presence of isopropanol. While Pt dissolution was marginally affected by the presence of isopropanol, several times higher Ru dissolution was detected, especially in the case of the Ru-rich compositions. Our results underline that trends in terms of electrocatalytic activity and stability cannot always be transferred from model samples to systems that are closer to the ones applied in real devices.

The widespread application of green hydrogen production technologies requires cost reduction of crucial elements. To achieve this, a viable pathway to reduce the iridium loading in proton exchange membrane water electrolysis (PEMWE) is explored. Herein, we present a scalable synthesis method based on a photodeposition process for a TiO2@IrOx core-shell catalyst with a reduced iridium content as low as 40 wt%. Using this synthesis route, we obtain titania support particles homogeneously coated with a thin iridium oxide shell of only 2.1 ± 0.4 nm. The catalyst exhibits not only high ex situ activity, but also decent stability compared to commercially available catalysts. Furthermore, the unique core-shell structure provides a threefold increased electrical powder conductivity compared to structures without the shell. In addition, the low iridium content facilitates the fabrication of sufficiently thick catalyst layers at decreased iridium loadings mitigating the impact of crack formation in the catalyst layer during PEMWE operation. We demonstrate that the novel TiO2@IrOx core-shell catalyst clearly outperforms the commercial reference in single-cell tests with an iridium loading below 0.3 mgIr cm 2 exhibiting a superior iridium-specific power density of 17.9 kW gIr-1 compared to 10.4 kW gIr-1 for the commercial reference.

Benzyltoluene (H0-BT) is a promising liquid organic hydrogen carrier (LOHC) molecule. Catalytic hydrogenation of H0-BT to perhydro benzyltoluene (H12-BT) and dehydrogenation back to H0-BT to release the chemically bound hydrogen constitute a suitable and technically relevant hydrogen storage cycle. Herein, we report the development of a bimetallic Pt-Re/Al2O3 catalyst for the dehydrogenation of H12-BT under moderate conditions to enable heat integration of the endothermal dehydrogenation reaction with low temperature waste heat streams. The reducibility of the catalyst is compared to a monometallic Pt/Al2O3 reference system using temperature-programmed reduction (TPR) and in situ reduction during X-ray absorption spectroscopy (XAS) to gain insight on the mode of interaction between Pt and Re. TPR and XAS propose full reduction of Pt, while rhenium oxide is only partially reduced at 400 degrees C. Analysis by means of extended X-ray absorption fine structure suggests a lower coordination number and thus smaller entities of Pt for bimetallic catalysts with increasing Re loading. Further, an electronic modification of Pt is observed, which mostly stems from residual Cl-species from the Pt-precursor, but may also indicate direct interaction with Re. Structural promotion of Pt by Re provided a strong stabilization of smaller clusters and nanoparticles leading to a high Pt dispersion even during catalyst activation in H2 at high temperatures of 700 degrees C. When compared to the monometallic reference, particularly the initial hydrogen release is accelerated when using Pt-Re/Al2O3 catalysts. Mechanistically, the bimetallic catalysts outperformed the monometallic reference catalyst due to an efficient initial dehydrogenation of H12-BT and a short lifetime of the partially dehydrogenated intermediate (H6-BT) yielding H0-BT as the desired product of the consecutive reaction. The catalytic performance and XAS studies suggest an optimized structural composition of the active Pt phase, potentially via an ensemble effect, which allows for efficient H2 release from H12-BT. H2 release from the liquid organic hydrogen carrier perhydro benzyltoluene (H12-BT) was accelerated using bimetallic Pt-Re/Al2O3 catalysts. An optimum Pt : Re ratio was identified and catalysts characterisation provided insight on Pt-Re interaction.

The formation kinetics of metal nanoparticles are generally described via mass transport and thermodynamics-based models, such as diffusion limited growth and classical nucleation theory (CNT). However, metal monomers are commonly assumed as precursors, leaving the identity of molecular intermediates and their contribution to nanoparticle formation unclear. Here we utilize liquid phase transmission electron microscopy (LPTEM) and reaction kinetic modeling to establish the nucleation and growth mechanisms and discover molecular intermediates during silver nanoparticle formation. Quantitative LPTEM measurements showed that their nucleation rate decreased while growth rate was nearly invariant with electron dose rate. Reaction kinetic simulations showed that Ag4 and Ag- followed a statistically similar dose rate dependence as the experimentally determined growth rate. We demonstrate that experimental growth rates are consistent with diffusion limited growth via attachment of these species to nanoparticles. Dose rate dependence of nucleation rate was inconsistent with CNT. We propose a reaction limited nucleation mechanism and demonstrate that experimental nucleation kinetics are consistent with Ag42+ aggregation rates at millisecond time scales. Reaction throughput analysis of the kinetic simulations uncovered formation and decay pathways mediating intermediate concentrations. The work demonstrates the power of quantitative LPTEM combined with kinetic modeling for establishing nanoparticle formation mechanisms and the principal intermediates.

Grading electrodes is a promising approach to reduce ohmic and mass transport-related voltage losses in proton exchange membrane fuel cells. In graded electrodes, the ionomer and/or catalyst are spatially non-uniformly distributed to optimize performance over a wide operating range. In this study, through-plane ionomer gradients were fabricated with a simple wet-layer deposition technique that can readily be adapted in a roll-to-roll process. The presence of ionomer gradients was verified using scanning transmission electron microscopy and the profiles were found to be continuous despite using only two coating steps. Single cell tests revealed that the gradients outperform conventional electrodes and maintain the optimal performance for different relative humidities. These improvements were traced back to enhanced mass transport and protonic conduction properties identified by detailed electrochemical analysis. This manufacturing approach for electrodes offers an accessible toolbox to produce versatile and specialized multi-layered catalyst layers for different applications. (c) 2024 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open accessarticle distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY,https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.

High-entropy alloys are claimed to possess superior stability due to thermodynamic contributions. However, this statement mostly lies on a hypothetical basis. In this study, we use on-line inductively coupled plasma mass spectrometer to investigate the dissolution of five representative electrocatalysts in acidic and alkaline media and a wide potential window targeting the most important applications. To address both model and applied systems, we synthesized thin films and carbon-supported nanoparticles ranging from an elemental (Pt) sample to binary (PtRu), ternary (PtRuIr), quaternary (PtRuIrRh), and quinary (PtRuIrRhPd) alloy samples. For certain metals in the high-entropy alloy under alkaline conditions, lower dissolution was observed. Still, the improvement was not striking and can be rather explained by the lowered concentration of elements in the multinary alloys instead of the synergistic effects of thermodynamics. We postulate that this is because of dissolution kinetic effects, which are always present under electrocatalytic conditions, overcompensating thermodynamic contributions.

Understanding catalyst dissolution pathways in protonexchangemembrane water electrolyzers is paramount for developing mitigationstrategies aiming toward higher durability and lower catalyst loadings.To this end, Ir dissolution has been extensively studied using aqueousmodel systems but not in real devices. Aiming to bridge this knowledgegap, we use a metal-free water electrolysis setup to determine themass balance of the dissolved Ir in an electrolyzer when applyinga protocol mimicking intermittent operation. We find that the mainIr sinks are the cathode catalyst layer and the membrane, while Irdissolution into the water lines is significantly lower. Althoughreproducible estimation of Ir present in the membrane is challenging,quantification of Ir within the cathode is reliable and efficient.This new finding implies that tracking Ir present in the cathode canbe used to estimate anode catalyst stability, thus accelerating catalystdevelopment and operational parameters optimization.

Photoelectrochemical (PEC) water splitting is a promising energy conversion technology based on the harvesting of sunlight to produce green hydrogen. One of the major challenges hindering the development of PEC devices is the stability of photoanodes since most semiconductors are susceptible to anodic decomposition in aqueous solutions. While hematite (a-Fe2O3 ) has been regarded as one of the most stable metal oxides to drive the oxygen evolution reaction in alkaline media, its photostability in a broad pH range is poorly investigated. In this work, we study the dissolution of model Fe2O3 thin films in different electrolytes, including unbuffered and buffered neutral, near-neutral, and alkaline solutions, using on-line PEC inductively coupled plasma mass spectrometry. Fe leaching is observed in all studied unbuffered electrolytes under irradiation while phosphate-buffered electrolytes reveal a dramatic stability enhancement at all pHs. The latter might imply that phosphate buffers either alleviate local acidification in the close vicinity of the electrode-electrolyte interface during the reaction or that specific adsorption of phosphate anions at the a-Fe2O3 surface could mitigate dissolution. Furthermore, we explore the long-term stability of a-Fe2O3 using a three-electrode bulk PEC cell. In the long run, phosphate buffers do not represent an optimal electrolyte choice either, as the surface Fe oxide gradually converts to Fe phosphates that are not photoelectrochemically active. Our work demonstrates that photocorrosion of Fe2O3 within electrolytes that are commonly used in the literature is not negligible and should be considered for designing stable semiconductor interfaces.

Liquid fuels are considered a promising alternative to hydrogen in proton exchange membrane fuel cells. In particular, isopropanol, which can be selectively oxidised to acetone and further hydrogenated back to isopropanol using electrochemical and heterogeneous catalysis routes, respectively, opens the possibility of zero-emission fuel cell operation without complex management of molecular H2. However, the maximum electric power of such fuel cells is still relatively low, which is attributed to the poisoning of state-of-the-art Pt-Ru electrocatalysts by adsorbed acetone and/or Ru oxide/hydroxide. Here, in order to mitigate Pt-Ru poisoning at higher anodic potentials during isopropanol oxidation in acidic media, the effect of the addition of Ir, a less oxophilic element than Ru, on the activity and stability during dynamic experiments of Pt-Ru is systematically investigated. To identify the most active compositions, Pt-Ru-Ir thin-film material libraries are prepared using magnetron co-sputtering. The electrocatalytic activity of the libraries is screened using a high-throughput scanning flow cell setup. Catalysts with the highest activity are further synthesised in the form of carbon-supported nanoparticles. Comparing the two systems, similar trends are observed, highlighting the model material libraries being an excellent starting point for novel catalyst development. Besides electrocatalytic activity, catalyst shelf-life and dissolution stability are studied. While significant ageing in the air is found, partial reactivation is possible using a reductive treatment. The dissolution of the most promising nanoparticulate electrocatalyst is evaluated using online inductively coupled plasma mass spectrometry to assess the effect of Ir addition on Pt and Ru stability. No significant stabilising role of Ir, however, is observed. Hence, further optimisation of Pt-Ru or Pt-Ru-Ir is still needed to improve isopropanol fuel cell performance.

In this work, we demonstrate RuP2-MoP catalysts being highly stable and selective for the dehydrogenation of long-chain alkanes like n-heptane. Compared to a monometallic MoP catalyst, the bimetallic system substantially increases n-heptene selectivity from 40% towards 80%. This effect can be traced back to a reduced surface acidity, suppressing the competitive hydrogenolysis reaction. The active transition metal phosphide is, furthermore, compared to its phosphorous-free RuMo-counterpart. As revealed by STEM-EDX investigations, incorporation of phosphorous results in the formation of separated metal phosphide clusters instead of an intermetallic alloy. In the dehydrogenation of n-heptane the phosphorous modification clearly avoids catalyst deactivation and maintains the high nheptene selectivity. X-ray diffraction, elemental analysis and STEM-EDX further reveal that catalyst coking and the formation of less active molybdenum carbide phases is effectively suppressed by phosphorous incorporation, making RuP2-MoP an attractive system for selective dehydrogenation of long-chain alkanes.