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

High-throughput exploration of activity and stability for identifying photoelectrochemical water splitting materials

The experimental high-throughput (HT) exploration for a suitable solar water splitting photoanode hasgreatly relied on photoactivity as the sole descriptor to identify a promising region within the searchedcomposition space. Although activity is essential, it is not sufficient for describing the overallperformance and excludes other pertinent criteria for photoelectrochemical (PEC) water splitting.Photostability in the form of (photo)electrocatalyst dissolution must be tracked to illustrate the intricaterelation between activity and stability for multinary photoelectrocatalysts. To access these two importantmetrics simultaneously, an automated PEC scanning flow cell coupled to an inductively coupled plasmamass spectrometer (PEC-ICP-MS) was used to study an Fe–Ti–W–O thin film materials library. Theresults reveal an interrelation between composition, photocurrent density, and element-specificdissolution. These structure–activity–stability correlations can be represented using data science toolslike principal component analysis (PCA) in addition to common data visualization approaches. This studydemonstrates the importance of addressing two of the most important catalyst metrics (activity andstability) in a rapid and parallel fashion during HT experiments to adequately discover high-performingcompositions in the multidimensional search space

Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS

High-impact photoelectrode materials for photoelectrochemical (PEC) water splitting are distinguished by synergistically attaining high photoactivity and stability at the same time. With numerous efforts toward optimizing the activity, the bigger challenge of tailoring the durability of photoelectrodes to meet industrially relevant levels remains. In situ photostability measurements hold great promise in understanding stability-related properties. Although different flow systems coupled to light-emitting diodes were introduced recently to measure time-resolved photocorrosion, none of the measurements were performed under realistic light conditions. In this paper, a photoelectrochemical scanning flow cell connected to an inductively coupled plasma mass spectrometer (PEC-ICP-MS) and equipped with a solar simulator, Air Mass 1.5 G filter, and monochromator was developed. The established system is capable of independently assessing basic PEC metrics, such as photopotential, photocurrent, incident photon to current efficiency (IPCE), and band gap in a high-throughput manner as well as the in situ photocorrosion behavior of photoelectrodes under standardized and realistic light conditions by coupling it to an ICP-MS. Polycrystalline platinum and tungsten trioxide (WO3) were used as model systems to demonstrate the operation under dark and light conditions, respectively. Photocorrosion measurements conducted with the present PEC-ICP-MS setup revealed that WO3 starts dissolving at 0.8 VRHE with the dissolution rate rapidly increasing past 1.2 VRHE, coinciding with the onset of the saturation photocurrent. The most detrimental damage to the photoelectrode is caused when subjecting it to a prolonged high potential hold, e.g., at 1.5 VRHE. By using standardized illumination conditions such as Air Mass 1.5 Global under 1 Sun, the obtained dissolution characteristics are translatable to actual devices under realistic light conditions. The gained insights can then be utilized to advance synthesis and design approaches of novel PEC materials with improved photostability

Photocorrosion of Hematite Photoanodes in Neutral and Alkaline Electrolytes

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 (α-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 α-Fe2O3 surface could mitigate dissolution. Furthermore, we explore the long-term stability of α-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.Fil: Benavente Llorente, Victoria. Helmholtz Institute Erlangen-nürnberg; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Jenewein, Ken J.. Helmholtz Institute Erlangen-nürnberg; Alemania. Universitat Erlangen Nuremberg; AlemaniaFil: Bierling, Markus. Helmholtz Institute Erlangen-nürnberg; Alemania. Universitat Erlangen Nuremberg; AlemaniaFil: Körner, Andreas. Helmholtz Institute Erlangen-nürnberg; Alemania. Universitat Erlangen Nuremberg; AlemaniaFil: Hutzler, Andreas. Helmholtz Institute Erlangen-nürnberg; Alemania. Universitat Erlangen Nuremberg; AlemaniaFil: Kormányos, Attila. University Of Szeged; HungríaFil: Cherevko, Serhiy. Helmholtz Institute Erlangen-nürnberg; Alemani

Photocorrosion of Hematite Photoanodes in Neutral and Alkaline Electrolytes

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 (α-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 α-Fe2O3 surface could mitigate dissolution. Furthermore, we explore the long-term stability of α-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

Electrolyte Engineering Stabilizes Photoanodes Decorated with Molecular Catalysts

Molecular catalysts are promising oxygen evolution promoters in conjunction with photoanodes for solar water splitting. Maintaining the stability of both photoabsorber and co-catalyst is still a prime challenge, with many efforts tackling this issue through sophisticated material designs. Such approaches often mask the importance of the electrode-electrolyte interface and overlook easily tunable system parameters, such as the electrolyte environment, to improve efficiency. We provide a systematic study on the activity-stability relationship of a prominent Fe2O3 photoanode modified with Ir molecular catalysts using in-situ mass spectroscopy. After gaining detailed insights into the dissolution behavior of the Ir co-catalyst, a comprehensive pH study is conducted to probe the impact of the electrolyte on the performance. An inverse trend in Fe and Ir stability is found, with the best activity-stability synergy obtained at pH 9.7. The results bring awareness to the overall photostability and electrolyte engineering when advancing catalysts for solar water splitting

Photocorrosion of Hematite Photoanodes in Neutral and Alkaline Electrolytes

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 (α-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 α-Fe2O3 surface could mitigate dissolution. Furthermore, we explore the long-term stability of α-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

Dissolution of WO 3 modified with IrO x overlayers during photoelectrochemical water splitting

WO3, an abundant transition metal semiconductor, is one of the most discussedmaterials to be used as a photoanode in photoelectrochemical water-splittingdevices. The photoelectrochemical properties, such as photoactivity and selectivityofWO3 in different electrolytes, are already well understood. However, theunderstanding of stability, one of the most important properties for utilizationin a commercial device, is still in the early stages. In this work, a photoelectrochemicalscanning flow cell coupled to an inductively coupled plasma massspectrometer is applied to determine the influence of co-catalyst overlayers onphotoanode stability. Spray-coatedWO3 photoanodes are used as a model system.Iridium is applied to the electrodes by atomic layer deposition in controlled layerthickness, as determined by ellipsometry and x-ray photoelectron spectroscopy.Photoactivity of the iridium-modifiedWO3 photoanodes decreases with increasingiridium layer thickness. Partial blocking of the WO3 surface by iridium isproposed as the main cause of the decreased photoelectrochemical performance.On the other hand, the stability ofWO3 is notably increased even in the presenceof the thinnest investigated iridium overlayer. Based on our findings, we providea set of strategies to synthesize nanocomposite photoelectrodes simultaneouslypossessing high photoelectrochemical activity and photostability