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

Navigating the Unkown With AI: Multiobjective Bayesian Optimization of Non-Noble Acidic OER Catalysts

Experimental catalyst optimization is plagued by slow and laborious efforts. Finding innovative materials is key to advancing research areas for sustainable energy conversion, such as electrocatalysis. Artificial intelligence (AI)-guided optimization bears great potential to autonomously learn from data and plan new experiments, identifying a global optimum significantly faster than traditional design of experiment approaches. Furthermore, it is vital to incorporate essential electrocatalyst features such as activity and stability into the optimization campaign to screen for a truly high-performing material. In this study, a multiobjective Bayesian optimization (MOBO) was used in conjunction with an experimental high-throughput (HT) pipeline to refine the composition of a non-noble Co-Mn-Sb-Sn-Ti oxide toward its activity and stability for the oxygen evolution reaction (OER) in acid. The viability of the MOBO algorithm was verified on a gathered data set, and an acceleration of 17x was achieved in subsequent experimental screening compared to a hypothetical grid search scenario. During the ML-driven assessment, Mn-rich compositions were critical to designing high-performing OER catalysts, while Ti incorporation into MnOx triggered an improved activity after short accelerated stress tests. To examine this finding further, an operando mass spectrometry technique was used to probe the evolution of activity, metal dissolution, and surface area over 3 h of operation. This work demonstrates the importance of respecting the multiobjective nature in electrocatalyst performance during HT campaigns. AI-based decision-making helps to bridge the gap between fast HT screening (limited property extraction) and slow fundamental research (rich property extraction) by avoiding less informative experiments

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

Photocorrosion of n‐ and p‐Type Semiconducting Oxide‐Covered Metals: Case Studies of Anodized Titanium and Copper

Illumination aects the corrosion of oxide-covered metals via photoinitiated dissolution processes. Anodized titanium with n-typesemiconducting anatase TiO2, and anodized copper with p-type semiconducting cuprite Cu2O of thicknesses up to ca. 90 nm areprepared, and investigated under controlled convection in photoelectrochemical experiments illuminated at grazing incidence. Il-lumination with photon energies above the band gap triggers anodic photocurrents for titanium above the at band potential, andcathodic photocurrents for copper below the at band potential. On both systems, increased corrosion rates are evidenced via mea-surements of polarization curves, electrochemical impedance spectra (EIS) and concentration determination via inductively coupledplasma mass spectrometry (ICP-MS). The increase in corrosion current with illumination is slightly lower than photocurrents, andscales linearly with intensity as expected if triggered by linear absorption. Following the Gerischer model, for titanium, electron-holepairs cause oxide dissolution by hole annihilation through cation dissolution. For copper, increased corrosion rates are caused by in-creased cathodic reaction rate through photoexcitation. The maximum non-thermal increase in corrosion rate is ca. 1 μA cm2 forcopper, and ca. 7 μA cm2 for titanium, thus few μm per year and negligible for structural materials. Photocorrosion may aect lo-calized corrosion, and nanostructures, e.g. if a morphology is crucial for a functional surface, such as in catalysts