Synthetic materials chemistry is the central foundation for advancing the design of solid-state electrocatalysts, where control over synthetic properties such as phase, composition, crystallinity, defect density, oxidation state, coordination environment, morphology, particle size, and electrical conductivity determine electrochemical performance descriptors. These descriptors include nature of active sites, number of active sites, mass and charge transport, and the local reaction environment, which collectively govern electrocatalytic peformance (ECP), namely activity, selectivity, and durability. In this review, we highlight the synthetic strategies currently employed in the electrocatalysis literature and show how they enable control over the properties of the in situ-formed active catalyst and its ECP. After highlighting the state of the art, we discuss how new developments in in situ analytics, data-driven discovery, and autonomous robotics could further improve the understanding, predictability, reproducibility, and throughput of materials synthesis. With these advancements, synthetic materials chemistry will remain a key driving force for electrocatalyst development.

ZUSAMMENFASSUNG Die synthetische Materialchemie bildet die zentrale Grundlage für die Weiterentwicklung des Designs von Festkörper‐Elektrokatalysatoren, wobei die Kontrolle über synthetische Eigenschaften wie Phase, Zusammensetzung, Kristallinität, Defektdichte, Oxidationszustand, Koordinationsumgebung, Morphologie, Partikelgröße und elektrische Leitfähigkeit elektrochemische Leistungsdeskriptoren wie die Natur der aktiven Zentren, die Anzahl aktiver Zentren sowie den Stoff‐ und Ladungstransport zusammen mit der lokalen Reaktionsumgebung bestimmt, welche wiederum Aktivität, Selektivität und Stabilität steuern. In diesem Übersichtsartikel heben wir die derzeit in der Elektrokatalyse verwendeten Synthesestrategien hervor und zeigen, wie diese genutzt werden können, um die Eigenschaften des in situ gebildeten aktiven Katalysators zu kontrollieren, die letztlich die elektrokatalytische Leistungsfähigkeit bestimmen. Nach der Darstellung, wie synthetische Chemie bislang zur Gestaltung elektrokatalytischer Leistung eingesetzt wurde, diskutieren wir, wie neue Entwicklungen in der in‐situ‐Analytik, datengetriebenen Entdeckung und autonomen Robotik das Verständnis, die Vorhersagbarkeit, die Reproduzierbarkeit und den Durchsatz der Materialsynthese weiter verbessern könnten. Mit diesen Fortschritten wird die synthetische Materialchemie eine zentrale treibende Kraft für die Entwicklung von Elektrokatalysatoren bleiben.

The development of efficient electrocatalysts for value-added organic oxidation reactions (OORs) is essential for sustainable chemical production and achieving carbon neutrality. In this work, we report a helical cobalt borophosphate...

Transition metal chalcogenides (TMCs) are among the most investigated precatalysts for alkaline oxygen evolution reaction (OER). However, the origins of their activity and the role of the nature of chalcogen atoms remain unclear. To address these questions, we developed analogous single-source precursors to synthesize structurally and morphologically alike CoS, CoSe, and CoTe phases, serving as ideal starting materials to isolate the chalcogens' role for the OER. We uncover the importance of reliable active site quantification, intrinsic activity evaluation, and monitoring in situ structural changes during OER. In our electrochemical analyses, special emphasis is placed on accurate redox activity evaluation. Our results show that the in situ-formed layered oxyhydroxide phases have similar intrinsic activities. The nature of the chalcogen atom influences the number of active sites, leading to the geometric activity trend: CoSe > CoS > CoTe. These insights are crucial for the understanding and development of future electrocatalysts and application-oriented devices.

Utilizing electrical energy for the targeted conversion of biomass into valuable molecules is a crucial building block for a future circular economy. Herein, a Nickel (Ni)-based conjugated metal-organic framework (MOF) having salicylaldehydate linkages (1, 3, 5-triformylphloroglucinol: Tp) was synthesized via a solid-state process. The resulting 2D framework (Ni-Tp) demonstrates a highly selective electrocatalytic conversion of 5-hydroxymethylfural (HMF) to 2, 5-furandicarboxylic acid (FDCA) with excellent faradaic efficiency (96 ± 4 %). In-situ Raman and X-ray absorption spectroscopy (XAS) reveal that Ni-Tp acts as a precatalyst for uniformly dispersed nickel (oxy)hydroxide (NiOOH) in the electrocatalytic organic oxidation reaction (OOR) process. The combination of efficient electron transport of the Ni-Tp and the uniform dispersion of newly formed nickel (oxy)hydroxide with excellent electrolyte availability leads to redox (and potentially catalytic) activity of all in situ formed nickel sites. Thus, the Ni-Tp is an ideal precatalyst in terms of nickel (oxy)hydroxide active site exposure. This work demonstrates a cost-effective method for synthesizing efficient MOF-based electrocatalysts for a relevant catalytic reaction.

Die Entdeckung neuer (Prä‐)Katalysatoren für die Sauerstoffentwicklungsreaktion (OER) mit außergewöhnlicher katalytischer Aktivität und Langzeitstabilität ist entscheidend für die Weiterentwicklung von Technologien zur Dekarbonisierung. In dieser Studie stellen wir die ternäre Ba8Ni6Ge40‐Phase mit einer Clathratstruktur vor, die eine bemerkenswerte Leistung in der alkalischen OER zeigt. Bei der Integration in einen alkalischen Wasserelektrolyseur erreicht dieser Clathrat‐Präkatalysator eine hohe Stabilität unter einer anhaltenden Stromdichte von ∼550 mA cm−2 über 10 Tage. Durch die Kombination von in‐situ‐Raman‐Spektroskopie, Quasi‐in‐situ‐Röntgenabsorptionsspektroskopie und (mikro)strukturellen Charakterisierungen klären wir die vollständige elektrochemische Rekonstruktion von Ba8Ni6Ge40 in ultradünne Nanoblätter auf. Diese bestehen aus einer porösen und defekten NiOOH‐Nanostruktur mit maximiertem Zugang zu den aktiven Zentren. Bemerkenswerterweise wurde auch ein reversibler Phasenübergang hauptsächlich zwischen Ni(OH)2 und NiOOH im elektrochemischen Redoxprozess nachgewiesen. Die erfolgreiche Anwendung des Modell‐Präkatalysators Ba8Ni6Ge40 stellt eine vielversprechende neue Klasse von funktionellen anorganischen Materialien für die Wasserelektrolyse dar.

Water-assisted electrocatalytic oxidation of alcohols into valuable chemicals is a promising strategy to circumvent the sluggish kinetics of water oxidation, while also reducing cell voltage and improving energy efficiency. Recently, transition metal (TM)-based catalysts have been investigated for anodic alcohol oxidation, but success has been limited due to competition from the oxygen evolution reaction (OER) within the working regime. In this study, NiCo-based Prussian blue analog (PBA) was electrochemically activated at the anodic potential to produce a Co-Ni(O)OH active catalyst with a nanosheet-like architecture. This catalyst was further employed for the selective oxidation of benzyl alcohol (PhCH2OH) to benzoic acid (PhCOOH), achieving a 97 % Faradaic efficiency (FE). The electrochemical activity of Co-Ni(O)OH was also compared with hydrothermally prepared CoNi-LDH, demonstrating that the PBA-derived Co-Ni(O)OH was more effective.

Discovering novel oxygen evolution reaction (OER) (pre)catalysts with exceptional catalytic activity and long‐term stability is pivotal for advancing technologies aimed at decarbonization. In this study, we present the ternary Ba8Ni6Ge40 phase with a clathrate structure exhibiting remarkable performance in alkaline OER. When integrated into an alkaline water electrolyzer, this clathrate precatalyst achieves high stability under a sustained current density of ~550 mA cm–2 for 10 days. By combining in‐situ Raman spectroscopy, quasi in‐situ X‐ray absorption spectroscopy, and (micro)structural characterizations, we elucidate the complete electrochemical transformation of Ba8Ni6Ge40 forming ultrathin nanosheets composed of a porous and defective NiOOH nanostructure with maximized accessible active site exposure. Notably, a reversible phase transition mainly between Ni(OH)2 and NiOOH has also been established in the electrochemical redox process. Meanwhile, the successful application of the model Ba8Ni6Ge40 precatalyst represents a promising new class of functional inorganic materials for water electrolysis.

Electrocatalytic research often emphasizes active site design. However, these sites realize their full potential only within an optimal local reaction environment. In a recent issue of Nature Chemical Engineering, Winter and colleagues demonstrate that ion-selective ionophores enhance nitrate reduction selectivity by retaining unwanted intermediates in the electrocatalyst’s local reaction environment.

The urgent need for efficient oxygen evolution reaction (OER) catalysts has led to the development and publication of many heterostructured catalysts. The application of such catalysts with multiple phases tremendously increases the material design dimensions, and numerous interface-related effects can tune the OER performance. In this regard, multiple of these heterostructured electrodes show remarkable OER activities. However, it is not clear if these carefully designed interfaces remain under prolonged OER conditions. Herein, a molecular approach is used to synthesize four different nickel-iron phosphide (heterostructured) materials and deposit them on fluorine-doped tin oxide and nickel foam electrodes. The OER performance of the eight electrodes and the reconstruction of the four materials is investigated by in-situ spectroscopy after one day of operation, enabled by a freeze-quench approach. The most active electrode is also applied under industrial OER conditions and for the value-added oxidation of alcohols to ketones. Before catalysis, this electrode comprises crystalline 4 nm nickel phosphide particles on an amorphous iron phosphide matrix. However, after 24 h, a homogenous nickel-iron oxyhydroxide phase has formed. This work questions to which extent the design of heterostructures is a suitable strategy for non-noble metal OER catalysis. This study investigates the potential of heterostructure design as a strategy for non-noble metal oxygen evolution reaction (OER), employing molecularly derived nickel-iron phosphide heterostructures as a model. The catalyst exhibits remarkable activity for OER and proves effective for the oxidation of alcohols to ketones. The (in)stability of these heterostructures are thoroughly assessed under operating conditions using advanced in-situ and ex-situ techniques. image

Jan Niklas Hausmann finished his PhD in 2022 and is currently a postdoc at the CatLab of the Helmholtz-Zentrum Berlin in the group of Prashanth W. Menezes. He is a trained inorganic chemist, and his research focuses on the development of electrocatalysts and structure-activity relations for conventional and hybrid water splitting. Furthermore, he is interested in the techno-economics of these electrocatalytic processes and has recently published an article titled “Is direct seawater splitting economically meaningful?”Lea R. Winter is an assistant professor in the Department of Chemical and Environmental Engineering at Yale University. She received a PhD in chemical engineering from Columbia University in 2020. She obtained postdoctoral training as a Nanotechnology Enabled Water Treatment (NEWT) Distinguished Postdoctoral Fellow at Yale in 2020–2022. Her research focuses on electrified processes at the food, energy, water, and climate nexus, including development of sustainable and circularized processes for conversion of CO2 to chemicals and fuels, green nitrogen fixation to fertilizers and nitrogen-based fuels, and transformation of contaminants in wastewater into useful products while recovering fit-for-purpose water.M.A. Khan is an assistant professor in the Chemical and Materials Engineering department at the University of Alberta. His research aims to contribute to a sustainable future through the development of innovative technologies that support zero-emission energy carriers like hydrogen and electricity. Dr. Khan’s approach integrates techno-economic analysis and life cycle analysis to model energy systems and net-zero transition pathways. His current contributions include advancements in the production of sustainable fuels and chemicals, impacting areas such as steel production and heavy-duty transportation. He has authored/coauthored 46 scientific articles and 4 government reports and has 6 granted US patents.Menachem Elimelech is the Sterling Professor of Chemical and Environmental Engineering at Yale University. His research interests include emerging membrane-based technologies at the water-energy nexus, materials for next-generation desalination and water purification membranes, and environmental applications of nanomaterials. Professor Elimelech is a Clarivate Analytics (formerly Thomson Reuters) Highly Cited Researcher. He is a member of the United States National Academy of Engineering and a foreign member of the Chinese Academy of Engineering, the Australian Academy of Technology and Engineering, and the Canadian Academy of Engineering.Md Golam Kibria is an associate professor at the Department of Chemical and Petroleum Engineering at the University of Calgary. He is the cofounder and CTO of several spin-off companies from the University of Calgary, including O-Two Carbon Inc., CarboMat Inc., and NetZero Hub Inc. Kibria has extensive expertise in electrochemical systems, including water electrolysis and CO2 electrolysis as well as electrochemical oxidation reactions. Furthermore, he is interested in process modeling and system-level analysis, including techno-economic and life cycle analysis, and has recently published an article titled “Seawater electrolysis for hydrogen production: A solution looking for a problem?”Tobias Sontheimer heads the Strategy Department for Energy and Information at the Helmholtz-Zentrum Berlin and has been helping to shape the transformation of the energy sector for more than 15 years. In his current role, he is responsible for research and development for green hydrogen technologies and sustainable aviation fuels. From 2014 to 2020, he was chief research manager for the Helmholtz Association’s national energy R&D portfolio. Sontheimer studied physics at RWTH Aachen University and Harvard University and completed his doctorate in the field of renewable energy technologies as a scholarship holder of SCHOTT AG.Prashanth W. Menezes is head of the Materials Chemistry Group for Thin-Film Catalysis at the CatLab of the Helmholtz-Zentrum Berlin and leads the Inorganic Materials Group at Technische Universität Berlin. He received his PhD from the Max Planck Institute for Chemical Physics of Solids in Dresden, after which he moved to Technische Universität München and then to Technische Universität Berlin to work on energy catalysis. His research focuses on the design, development, and dynamic structural understanding of novel functional precatalysts in heterogeneous catalysis, especially for applications in redox oxygen catalysis, (photo)electrocatalytic water splitting, and electrochemical redox reactions.

Nickel mesh (NM) is used in industrial alkaline water electrolyzers due to its cost-effectiveness and conductivity. However, the decisive factors that advance the efficiency and sustainability of such electrodes are only partially understood. Herein, an efficient NM-based electrocatalyst for the oxygen evolution reaction is developed via a single-step nitridation route on a commercially used NM substrate and sheds light on the role of reconstruction and iron content to boost catalyst performance and durability. Remarkably, the activated Ni3N/NM catalyst required an overpotential of 0.46 V to deliver 1 A cm(-2) in ambient conditions (1 M KOH, 25 degrees C). This overpotential decreases substantially to 0.28 V in industrially relevant conditions (6 M KOH, 85 degrees C) and is maintained for 235 h. Ni3N/NM partially transformed into NiFe layered (oxy)hydroxide in both conditions, while the active structure's Fe content is reconstruction condition dependent (temperature and KOH concentration). Electrodes reconstructed under industrially relevant conditions performed better than ambient reconstructed ones due to a more pronounced iron-incorporation from KOH and the evolution of porous morphologies. In industrial environments, activated Ni3N/NM excels in selectively converting benzyl alcohol to benzoic acid, achieving an impressive yield of 96%.

High-entropy materials (HEMs) offer a quasi-continuous spectrum of active sites and have generated great expectations in fields such as electrocatalysis and energy storage. Despite their potential, the complex composition and associated surface phenomena of HEMs pose challenges to their rational design and development. In this context, we have synthesized FeCoNiPdWP high entropy phosphide (HEP) nanoparticles using a low-temperature colloidal method, and explored their application as bifunctional electrocatalysts for the oxygen evolution and reduction reactions (OER/ORR). Our analysis provides a detailed understanding of the individual roles and transformations of each element during OER/ORR operation. Notably, the HEPs exhibit an exceptionally low OER overpotential of 227 mV at 10 mA cm-2, attributed to the reconstructed HEP surface into a FeCoNiPdW high entropy oxyhydroxide with high oxidation states of Fe, Co, and Ni serving as the active sites. Additionally, Pd and W play crucial roles in modulating the electronic structure to optimize the adsorption energy of oxygen intermediates. For the ORR, Pd emerges as the most active component. In the reconstructed catalyst, the strong d-d orbital coupling of especially Pd, Co, and W fine-tunes ORR electron transfer pathways, delivering an ORR half-wave potential of 0.81 V with a pure four-electron reduction mechanism. The practicality of these HEPs catalysts is showcased through the assembly of aqueous zinc-air batteries. These batteries demonstrate a superior specific capacity of 886 mA h gZn-1 and maintain excellent stability over more than 700 hours of continuous operation. Overall, this study not only elucidates the role of each element in HEMs but also establishes a foundational framework for the design and development of next-generation bifunctional oxygen catalysts, broadening the potential applications of these complex materials in advanced energy systems. FeCoNiPdWP exhibit excellent oxygen evolution and reduction reaction performance via all elements playing distinctive roles and the switchable active sites in redox reactions, leading to robust zinc air batteries.

Merely all transition-metal-based materials reconstruct into similar oxyhydroxides during the electrocatalytic oxygen evolution reaction (OER), severely limiting the options for a tailored OER catalyst design. In such reconstructions, initial constituent p-block elements take a sacrificial role and leach into the electrolyte as oxyanions, thereby losing the ability to tune the catalyst's properties systematically. From a thermodynamic point of view, indium is expected to behave differently and should remain in the solid phase under alkaline OER conditions. However, the structural behavior of transition metal indium phases during the OER remains unexplored. Herein, are synthesized intermetallic cobalt indium (CoIn3) nanoparticles and revealed by in situ X-ray absorption spectroscopy and scanning transmission microscopy that they undergo phase segregation to cobalt oxyhydroxide and indium hydroxide. The obtained cobalt oxyhydroxide outperforms a metallic-cobalt-derived one due to more accessible active sites. The observed phase segregation shows that indium behaves distinctively differently from most p-block elements and remains at the electrode surface, where it can form lasting interfaces with the active metal oxo phases.

Electrocatalytic systems are enormously challenging to understand. Nevertheless, the complexity of systems reported in the literature constantly increases, with frequent reports on heterostructured electrodes containing multiple interfaces. As current electrochemical and analytical methods can hardly meet this complexity, fundamental catalytic aspects often remain elusive, e.g., intrinsic activity, number of active sites, surface area, in-situ structure, etc. Nonetheless, complex interface-related hypotheses are postulated. Herein, we describe a pathway with essential electrocatalytic and analytical points that must be addressed before meaningful ab initio (mainly density functional theory, DFT) models and new hypotheses are raised. It comprises three parts: (i) determining if the activity changed intrinsically, (ii) revealing the in-situ composition, and (iii) identifying the active sites and the reaction mechanism. We anticipate that this perspective helps authors and reviewers acknowledge electrocatalysis' tremendous complexity and provides a systematic pathway to check if fundamental aspects are covered before complex, potentially misleading hypotheses are raised.

Iron‐based (pre)catalysts have attracted enormous attention for various electrooxidation reactions due to the low cost, high abundance, and multiple accessible redox states of iron. Herein, a well‐defined helical iron borophosphate (LiFeBPO) is developed as an electro(pre)catalyst for the oxygen evolution reaction (OER) and selective alcohol oxidation. When deposited on nickel foam (NF), LiFeBPO exhibits an exceptional OER performance at ambient conditions attaining a current density of 100 mA cm −2 at ≈276 mV overpotential in 1 m KOH. Notably, this anode sustains durable alkaline water electrolysis at 500 mA cm −2 for over 330 h under industrial conditions (6 m KOH and 85 °C). In –situ and ex situ investigations reveal a deep reconstruction of LiFeBPO during OER, which transforms into a 3D open porous skeleton assembled by ultrasmall, low‐crystalline α‐FeOOH nanoparticles (interfacing with NiOOH of NF). This structure contributes to exposing accessible surface active sites, as well as accelerating mass transport and bubble detachment. Moreover, this electrode also catalyzes the electrooxidation of alcohols (methanol, ethylene glycol, and glycerol) to formic acid (FA) with high selectivity and full conversion. This study provides promising solutions for designing suitable anodes for the simultaneous production of green hydrogen fuel and value–added FA from electrooxidation reactions.

Electrochemical production of large-scale chemicals and fuels is critical to reaching carbon neutrality. However, the required anodic oxidation reactions, namely the oxygen evolution reaction (OER) or the oxidation of organics into value-added products, suffer from large overpotentials. To address this challenge, researchers have been widely investigating non-water-soluble (pre)catalysts to operate in the aqueous electrolyte. On the contrary, in this work, we approach a rapid, easy, and green carbon cloth electrode preparation using merely water-soluble nitrate precursors and ethanol as chemicals and no heating steps. The drop-coated, water-soluble transition metal salts reconstruct rapidly into the respective oxyhydroxides under OER conditions, with the oxyanion acting as a beneficial sacrificial reagent. This approach is shown herein for nickel(-iron) catalysts and their successful application for the OER (220 mV overpotential at 10 mA cm-2, long-term stability of 40 h at 100 mA cm-2) and the oxidation of 5-hydroxymethylfurfural (HMF, quantitative faradaic efficiency). We compare both reactions with both electrodes closely and find that the iron-free sample is more active for the HMF oxidation in regimes where mass transport is not the main limiting factor. We anticipate that this simple electrode preparation approach can find wide application in electrocatalysis and beyond. We report on a rapid, green, and cost-effective fabrication of nickel(-iron) oxyhydroxides by drop-coating and reconstructing water-soluble nitrate precursors, and their application for the OER and the oxidation of 5-hydroxymethylfurfural (HMF).

Cobalt‐iron oxyhydroxides (CoFeOOH x ) are among the most active catalysts for the oxygen evolution reaction (OER). However, their redox behavior and the electronic and chemical structure of their active sites are still ambiguous. To shed more light on this, the complete and rapid reconstruction of four helical cobalt‐iron borophosphates with different Co:Fe ratios into disordered cobalt‐iron oxyhydroxides can be achieved, which are electrolyte‐penetrable and thus most transition metal sites can potentially participate in the OER. To track the redox behavior and to identify the active structure, quasi in situ X‐ray absorption spectroscopy is applied. Iron in high oxidation states ≥ IV (Fe 4+ ) and its substantial redox behavior with an average oxidation state of around 2.8 to above 3.2 is detected. Furthermore, a 6% contraction of the Fe‐O bond length compared to Fe 3+ OOH references is observed during OER and a strong distortion of the [MO 6 ] octahedra is identified. It is hypothesized that this bond contraction is caused by the presence of oxyl radicals and that di‐µ‐oxyl radical bridged cobalt‐iron centers are the active sites. It is anticipated that the detailed electronic and structural description can substantially contribute to the debate on the nature of the active site in bimetallic iron‐containing OER catalysts.

To enable a future society based on sun and wind energy, transforming electricity into chemical energy in the form of fuels is crucial. This transformation can be achieved in an electrolyzer performing water splitting, where at the anode, water is oxidized to oxygen—oxygen evolution reaction (OER)—to produce protons and electrons that can be combined at the cathode to form hydrogen—hydrogen evolution reaction (HER). While hydrogen is a desired fuel, the obtained oxygen has no economic value. A techno‐economically more suitable alternative is hybrid water electrolysis, where value‐added oxidation reactions of abundant organic feedstocks replace the OER. However, tremendous challenges remain for the industrial‐scale application of hybrid water electrolysis. Herein, these challenges, including the higher kinetic overpotentials of organic oxidation reactions compared to the OER, the small feedstock availably and product demand of these processes compared to the HER (and carbon dioxide reduction), additional purifications costs, and electrocatalytic challenges to meet the industrially required activities, selectivities, and especially long‐term stabilities are critically discussed. It is anticipated that this perspective helps the academic research community to identify industrially relevant research questions concerning hybrid water electrolysis.