Automated high-throughput activity and stability screening of electrocatalysts

Common high throughput (HT) approaches rapidly assess the activity of electrocatalyst libraries towards electrochemical conversion reactions. The short time regime on which individual measurements are performed creates a false perception of catalyst durability, masking the true catalyst performance by omission of detailed stability assessments during HT campaigns. Here, an automated scanning flow cell coupled to an inductively coupled plasma mass spectrometer was developed, allowing a simultaneous HT determination of the catalyst activity and stability. Fe-Ni and Fe-Ni-Co oxide libraries were automatically synthesized by a custom-programmed pipetting robot and examined as an oxygen evolution catalyst in neutral media, the advancement of which remains a great challenge. Ni-rich compositions in Fe-Ni oxides show higher activity but also significant catalyst loss due to the major Ni dissolution, which triggers Fe dissolution. Co-rich compositions in Fe-Ni-Co oxides attain the best synergy between activity and stability.High Throughput, ICP-MS, Scanning Flow Cell, In-Situ Stability, Liquid-Handling Robot, Automation, Oxygen Evolution, Transition Metal Oxide

Influence of fuels and pH on the dissolution stability of bifunctional PtRu/C alloy electrocatalysts

The application of organic fuels in fuel cells is an attractive way to circumvent the major drawbacks of hydrogen as an energy carrier, yet catalysis is still a bottleneck for efficient oxidation. One of the most promising bifunctional anode catalysts is PtRu, which has proven to be the state-of-the-art electrocatalyst in alcohol oxidation processes. While plenty of works so far have addressed activity and mechanism of oxidation reactions on PtRu, less is known about the influence of organic fuels on the stability during operation. In this contribution, the effect of isopropanol, methanol, ethanol, formic acid, ammonia, and carbon monoxide on the stability of carbon-supported PtRu was studied both in acidic and alkaline media. The scanning flow cell coupled to an inductively coupled plasma mass spectrometer (on-line ICP-MS) technique allowed the tracking of dissolution events that occurred during the applied electrochemical protocol in real-time. Our main conclusion is that PtRu/C remained stable in the operation range of fuel cells. In addition, if the upper potential limit was further increased PtRu/C was less stable in alkaline medium in which, if compared to acidic electrolyte, approximately 4-times higher Ru and 14-times higher Pt dissolution was measured in the absence of the studied fuels. The onset potential of dissolution was not affected by the presence of fuels (except CO), while dissolution rates were notably affected, most visibly in the case of isopropanol and ammonia in alkaline media and carbon monoxide in both acidic and alkaline media. The observed phenomena are briefly discussed underlining the necessity of more detailed and mechanistic studies to fully understand the reason behind dissolution processes in the presence of the investigated fuels

Performance of quaternized polybenzimidazole-cross-linked poly(vinylbenzyl chloride) membranes in HT-PEMFCs

High-temperature proton-exchange membrane fuel cells (HT-PEMFCs) are mostly based on acid-doped membranes composed of polybenzimidazole (PBI). A severe drawback of acid-doped membranes is the deterioration of mechanical properties upon increasing acid-doping levels. Cross-linking of different polymers is a way to mitigate stability issues. In this study, a new ion-pair-coordinated membrane (IPM) system with quaternary ammonium groups for the application in HT-PEMFCs is introduced. PBI cross-linked with poly(vinylbenzyl chloride) and quaternized with three amines (DABCO, quinuclidine, and quinuclidinol) are manufactured and compared to the state-of-the-art commercial Dapazol PBI membrane ex situ as well as by evaluating their HT-PEMFC performance. The IPMs show reduced swelling and better mechanical properties upon doping, which enables a reduction in membrane thickness while maintaining a comparably low gas crossover and mechanical stability. The HT-PEMFC based on the best-performing IPM reaches up to 530 mW cm–2 at 180 °C under H2/air conditions at ambient pressure, while Dapazol is limited to less than 430 mW cm–2 at equal parameters. This new IPM system requires less acid doping than conventional PBI membranes while outperforming conventional PBI membranes, which renders these new membranes promising candidates for application in HT-PEMFCs

Atomistic insights into activation and degradation of La0.6Sr0.4CoO3 ẟ electrocatalysts under oxygen evolution conditions

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role for their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electro-catalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3-ẟ under steady-state OER conditions. Using a multi-scale micros-copy and spectroscopy approach, we identify evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, that can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface results in the failure of the perovskite catalyst under applied potential

Rapid one-pot synthesis and photoelectrochemical properties of copper vanadates

Solution combustion synthesis (SCS) is shown to be versatile for the rapid-one-pot synthesis of three compounds and four polymorphs in the Cu-V-0 ternary family: alpha-CuV2O6, alpha- and beta-Cu2V2O7, and gamma-Cu3V2O8. These compounds feature copper/vanadium stoichiometric ratios ranging from 1:1 to 3:1; their structural, electronic, optoelectronic, and photoelectrochemical attributes were comprehensively characterized by a combination of theoretical and experimental techniques. The main contribution of the present study is the demonstration that a range of stoichiometries in this compound family can be derived simply by tuning the precursor mole ratio in the SCS procedure. The Cu-V-O family of samples, derived by SCS, is shown to exemplify the strong effect of compound stoichiometry on the optoelectronic and photoelectrochemical properties. Overall, alpha-CuV2O6 showed the best performance, rooted in the direct nature of the optical transition in this material. Finally, SCS is very time-efficient and the various compositions can be obtained in a matter of minutes, as opposed to hours or even days in classical solution-based or ceramic synthesis routes2428372847COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES88881.131530/2016-0C.J. and A.K. acknowledge the support of the“Széchenyi 2020”program within the framework of the GINOP-2.3.2-15-2016-00013 project. M.T.G. and C.L. acknowledge CAPES-PDSE(Process#88881.131530/2016-0) for partial financial supportunder the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Program. M.N.H. was supported by the National Science Foundation (Award No. DMR-1609811).M.N.H. and H.P.S. thank the Texas Advanced ComputingCenter (Austin, TX) facility for their computational needs.The authors thank the three anonymous reviewers forperceptive comments on an earlier version of this manuscrip

On the electrocatalytical oxygen reduction reaction activity and stability of quaternary RhMo-doped PtNi/C octahedral nanocrystals

Recently proposed bimetallic octahedral Pt–Ni electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) cathodes suffer from particle instabilities in the form of Ni corrosion and shape degradation. Advanced trimetallic Pt-based electrocatalysts have contributed to their catalytic performance and stability. In this work, we propose and analyse a novel quaternary octahedral (oh-)Pt nanoalloy concept with two distinct metals serving as stabilizing surface dopants. An efficient solvothermal one-pot strategy was developed for the preparation of shape-controlled oh-PtNi catalysts doped with Rh and Mo in its surface. The as-prepared quaternary octahedral PtNi(RhMo) catalysts showed exceptionally high ORR performance accompanied by improved activity and shape integrity after stability tests compared to previously reported bi- and tri-metallic systems. Synthesis, performance characteristics and degradation behaviour are investigated targeting deeper understanding for catalyst system improvement strategies. A number of different operando and on-line analysis techniques were employed to monitor the structural and elemental evolution, including identical location scanning transmission electron microscopy and energy dispersive X-ray analysis (IL-STEM-EDX), operando wide angle X-ray spectroscopy (WAXS), and on-line scanning flow cell inductively coupled plasma mass spectrometry (SFC-ICP-MS). Our studies show that doping PtNi octahedral catalysts with small amounts of Rh and Mo suppresses detrimental Pt diffusion and thus offers an attractive new family of shaped Pt alloy catalysts for deployment in PEMFC cathode layers

Atomistic Insights into Activation and Degradation of La 0.6 Sr 0.4 CoO 3−δ Electrocatalysts under Oxygen Evolution Conditions

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role in their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electrocatalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3−δ under steady-state OER conditions. Using a multiscale microscopy and spectroscopy approach, we identify the evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, which can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface result in the failure of the perovskite catalyst under applied potential

Atomistic Insights into Activation and Degradation of La_0.6Sr_0.4CoO_3−δ Electrocatalysts under Oxygen Evolution Conditions

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role in their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electrocatalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3−δ under steady-state OER conditions. Using a multiscale microscopy and spectroscopy approach, we identify the evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, which can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface result in the failure of the perovskite catalyst under applied potential

Atomistic Insights into Activation and Degradation of La_0.6Sr_0.4CoO_3−δ Electrocatalysts under Oxygen Evolution Conditions

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role in their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electrocatalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3−δ under steady-state OER conditions. Using a multiscale microscopy and spectroscopy approach, we identify the evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, which can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface result in the failure of the perovskite catalyst under applied potential