Tuning the oxygen evolution reaction activity of Co3O4 nanocubes via controlled metal doping and surface faceting Hatem M.A. Amin, Carsten Placke-Yan, Georg Bendt, Ulrich Hagemann, Stephan Schulz Chemical Engineering Journal, 2026 Water electrolysis is a critical component of green hydrogen production and energy storage and transformation. However, the sluggish kinetics of the four-electron oxygen evolution reaction (OER) hinder this process, which therefore requires effective catalysts. In recent years, there has been increasing interest in tuning the OER activity of spinel-type mixed-transition metal oxide catalysts by controlling their electronic structure (via doping) and surface structure (morphology) as well as cation diffusion (oxygen vacancy). In this study, we report the controlled synthesis of M 0.1 Co 2.9 O 4 nanocubes of similar size and comparable dopant concentrations with redox-active and -inactive divalent (M = Mn, Zn) and trivalent (M = Cr) metal cations via a robust hydrothermal process. This allows for a direct structure-activity correlation for OER in 1.0 M KOH electrolyte. Cr doping was found to promote the OER activity by lowering the overpotential for the Cr 0.1 Co 2.9 O 4 nanocubes by 115 mV compared to undoped Co 3 O 4 nanocubes, thus achieving a comparable overpotential to benchmark catalysts, whereas Mn doping showed a detrimental catalytic effect. Calcining Cr-doped nanocubes (Cr 0.1 Co 2.9 O 4 ) resulted in Cr segregation to the outer 20 nm surface of the resulting Cr 0.1 Co 2.9 O 4 -calc nanocubes as proven by XPS depth profiling and HR-TEM imaging. Cr 0.1 Co 2.9 O 4 -calc nanocubes exhibit lower OER activity than the untreated Cr 0.1 Co 2.9 O 4 nanocubes; however, they are still more active than the undoped Co 3 O 4 nanocubes. While no morphological or particle size changes were observed in the particles after OER, electronic surface transformations were detected post-catalysis using XPS. This work demonstrates the crucial role of the bulk and surface composition, metal segregation, and electronic structure of cobalt spinel electrocatalysts in OER and therefore contributes to the rational design of nanocatalysts for water electrolysis. • Facile synthesis of size- and composition-controlled M₀.₁Co₂.₉O₄ nanocubes without organic capping agent. • Distinct dopant-dependent OER performance is revealed, with Cr doping significantly boosting activity. • OER activity tuning is directly linked to electronic structure modulation, particularly surface Co 2+ content • Low-temperature calcination-induced Cr segregation alters surface composition and electronic structure. • Revealed critical roles of bulk/surface composition, metal segregation, and electronic structure in governing OER activity
Characterizing nanostructured films using phase sensitive vibrational sum frequency spectroscopy Furong Yan, Carsten Placke-Yan, Aleyna Yasar, Zhipeng Huang, Gerd Bacher, Stephan Schulz, Yujin Tong, R. Kramer Campen Journal of Chemical Physics, 2026 Nanoparticle films are ubiquitous thermal and electrocatalysts, yet their operando characterization remains challenging. Vibrational sum-frequency generation (vSFG) spectroscopy offers unique advantages due to its high sensitivity and surface specificity, but its application to systems with such intermediate length scale disorder, particularly with phase-resolved detection, has been challenging. In this study, we describe an approach to phase-resolved vSFG spectroscopy of nanoparticle films using z-cut α-quartz as a local reference. We show, by analysis of an octadecyltrichlorosilane film on quartz under the ppp polarization condition, that quantitative detection of absolute phase is possible and subsequently apply this protocol to a film of Mn-doped Co3O4 nanoparticles. Two OH species are resolved (∼3585 and ∼3770cm−1), both oriented H-up relative to the surface. This approach delivers a practical, internally referenced, phase-resolved vSFG methodology for nanoparticle ensembles on dielectric supports and, therefore, offers operando access to catalytic interfaces beyond metallic or plasmonically enhanced systems.
Multinuclear Mixed-Valent Co-Oxido Complexes: Synthesis, Structure, Magnetic, and Electrochemical Properties Surendar Karwasara, Xiang Ma, Hatem M. A. Amin, Timo Fockenberg, Gaurav Kanu, Christoph Wölper, Sabrina Disch, Stephan Schulz Inorganic Chemistry, 2026 A series of mixed-valent, multinuclear cobalt-oxido clusters [CoIIICoII2(mdea)3(H2mdea)]ClO4 (1), [CoIII2CoII2(mdea)4(DAA)2](BPh4)2 (2), [CoIII3CoII4(mdea)6(NO3)3](NO3)2 (3), [CoIII3CoII4(mdea)6(fa)3](ClO4)2 (4), [Na2CoIII4CoII4(mdea)6(CO3)4(OH)2(H2O)2] (5), [CoIII3CoII7(mdea)6(fa)5(OH)4](ClO4)3 (6), and [CoIII4CoII9(mdea)8(NO3)4(OH)8](NO3)2 (7) containing up to 13 Co atoms were synthesized and structurally characterized using single-crystal X-ray diffraction as well as FT-IR and UV–vis spectroscopy. The cobalt-oxido clusters contain N-methyldiethanolamine (H2mdea) as a stabilizing ligand and feature Co3O4 (1), Co4O6 (2), Co7O12 (3, 4), Na2Co8O18 (M10O18) (5), Co10O16 (6), and Co13O24 (7) scaffolds. The increasing number of Co cations in the cobalt-oxido cores of compounds 1–7 results from the systematic addition of pseudocubane Co3O4 units and the progressive incorporation of hydroxide ligands. The water oxidation activity and electrochemical properties of the CoII/CoIII centers in the complexes were studied by cyclic voltammetry (CV), while their magnetic properties were investigated via temperature-dependent magnetic susceptibility.
Comparative Study on the Catalytic Activity of Molecular [Co4IIIO4] Heterocubanes in Alcohol Oxidation Reactions in Solution Timo Fockenberg, Niklas Sülzner, Takuma Sato, Dongsheng Zhang, Akhil Hareendran, Jill M. Reher, Joana Tewes, Alexander Schnegg, Martin Muhler, Christof Hättig, Stephan Schulz ACS Catalysis, 2026 A comparative study on the catalytic oxidation of 2-propanol ( i -PrOH), benzyl alcohol (BnOH), and cinnamyl alcohol (CnOH) in solution under moderate reaction conditions (65–150 °C) using two tetranuclear Co III -oxo complexes [Co 4 O 4 (O 2 CR) 4 (py) 4 ] (R = Me 1, Et 2, py = pyridine) and three different oxidants (O 2, H 2 O 2, tert -butyl hydroperoxide (TBHP)) is reported. TBHP is the most active oxidant, resulting in turnover frequency (TOF) values ranging from 40 to 100 h –1 . The slightly larger carboxylate ligand in complex 2 favors aldehyde selectivity but slightly decreases the conversion rates as was confirmed by GC analyses. Mechanistic investigations ( in situ 1 H NMR, EPR) confirm the active participation of transiently formed radicals in these reactions. Using quantum-chemical calculations, a detailed mechanistic understanding of the catalytic reactions was gained that fully agrees with the experimental observations. Two interrelated catalytic cycles were identified: one for the oxidant activation and one for the alcohol oxidation. Catalytic TBHP oxidation reactions are initiated via Haber-Weiss activation of TBHP, resulting in the formation of tert -butyl peroxyl radicals ( t -BuOO • ), and simultaneous reduction of Co III to Co II .
Light on: Impact of Reaction Conditions and Catalyst Synthesis in Co3O4-Catalyzed Aerobic Oxidation of Ethylene Glycol Catalina Leiva-Leroy, Yuheng Jiang, Carsten Placke-Yan, Jean Pascal Fandre, Leon Müller, G. Wilma Busser, Dongsheng Zhang, Akhil Hareendran, Meltem Topcu, Hartmut Wiggers, Christof Schulz, Harun Tüysüz, Stephan Schulz, Bastian Mei, Martin Muhler ACS Applied Energy Materials, 2026 The transition to a sustainable chemical industry necessitates processes that utilize renewable feedstocks and energy sources. The selective oxidation of biobased ethylene glycol (EG) to valuable chemicals like glycolic acid as a precursor for bioplastics and formic acid as a hydrogen carrier represents a promising pathway. However, conventional methods often rely on noble metals or unsustainable oxidants. This study explores the potential of non-noble Co3O4 catalysts, synthesized via coprecipitation (CP), hard templating (HT), and spray-flame synthesis (SF), for the thermal and photothermal oxidation of EG. We demonstrate that the synthesis method profoundly impacts catalytic performance and catalyst stability. The SF-derived catalyst exhibited superior initial activity, while the HT catalyst showed exceptional reusability without or only minor deactivation. In addition, it is highlighted that the introduction of light as an additional stimulus significantly enhanced EG conversion by direct utilization of photogenerated charge carriers. Moreover, using illumination, C–C bond cleavage leading to the formation of formic acid appears to be less dominant compared to rate enhancements obtained by higher reaction temperatures. Thus, higher selectivity for the formation of glycolic acid is maintained. Postcatalytic characterization of the catalyst revealed that catalyst deactivation is linked to structural changes and the catalyst’s inability to reoxidize Co2+ sites back to active Co3+. This work provides fundamental insight into the rational design of robust, non-noble metal oxide catalysts and demonstrates photothermal catalysis as a powerful strategy for advancing sustainable liquid-phase oxidation reactions.
Double E─H Bond Activation of Ammonia and Water by Cyclic Gallaphosphene L(OCP)GaPGaL Mahendra K. Sharma, Christoph Wölper, Gebhard Haberhauer, Stephan Schulz Angewandte Chemie International Edition, 2026 Cyclic gallaphosphene L(PCO)GaPGaL 1 (L = HC[C(Me)NAr] 2 ; Ar = 2,6‐ i ‐Pr 2 ‐C 6 H 3 ) selectively reacts with NH 3 and H 2 O at ambient temperature with twofold N─H and O─H bond activation and formation of compounds LGa(μ‐PH)(μ‐NHC(O)PH)GaL 2 and LGa(μ‐PH)(μ‐OC(O)PH)GaL 3 . Both nucleophilic P atoms of 1 are protonated in these reactions, while the electrophilic carbon atom of the bridging PCO unit binds to the remaining NH group / O atom. The formation of heterocycles 2 and 3 , which were characterized by heteronuclear NMR ( 1 H, 13 C{ 1 H}, 31 P{ 1 H}) and IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction (sc‐XRD), is only possible due to a beneficial interplay between the polar Ga─P double bond and the electrophilic nature of the C center in the bridging PCO unit. The reaction mechanism and energetics of the NH 3 reaction was investigated in detail by quantum chemical calculations, which also highlight the importance of bimolecular reaction processes with the involvement of an additional NH 3 molecule.
Interfacial Softening and Electrolyte Uptake in Co3O4 OER Catalysts: Insight from Operando Spectroscopy and Fast EQCM-D Christian Leppin, Carsten Placke‐Yan, Georg Bendt, Sheila Hernandez, Kristina Tschulik, Stephan Schulz, Julia Linnemann Chemcatchem, 2026 Cobalt spinel (Co 3 O 4 ) catalysts are widely studied in scope of the electrocatalytic oxygen evolution reaction (OER), yet the role of interfacial structural transformation under anodic bias remains under debate. Here, we employ an operando approach, combining a fast electrochemical quartz crystal microbalance with dissipation monitoring (EQCM‐D), electrochemical impedance spectroscopy (EIS), and Raman spectroscopy to investigate interfacial transformations of Co 3 O 4 nanoparticle electrodes in alkaline electrolyte. We identify two distinct regimes during the anodic sweep prior to the macroscopic OER onset. At lower potentials, the catalyst interface remains mechanically rigid while reversibly associating several OH − /H 2 O species per oxidized cobalt site. At higher potentials, pronounced softening of the interface occurs alongside further uptake of electrolyte species. This indicates amorphization and a ‘swelling process’ beyond simple adsorption. Notably, an electrochemical conditioning treatment can suppress mass and compliance hysteresis without affecting OER activity, suggesting that most incorporated electrolyte species do not participate in the OER. EIS further reveals that OER intermediates form well below the apparent OER onset potential. These results advance our mechanistic understanding of interfacial transformations in cobalt‐based OER catalysts and establish EQCM‐D as a sensitive operando technique for probing electrocatalyst transformations.
Mechanistic Understanding of Laser-Induced Defect Engineering of Anisotropic Cobalt Oxide Spinel Platelets in Water Dana Schellenburg, Thomas Bihnam, Carsten Placke‐Yan, Georg Bendt, Oleg Prymak, Takuma Sato, Dylan Jennings, Catalina Leiva‐Leroy, Dongsheng Zhang, Milen Nachev, Kapil Dhaka, Falonne Nkou, Ulrich Hagemann, Markus Heidelmann, Stephane Kenmoe, Kai S. Exner, Bernd Sures, Martin Muhler, Christian H. Liebscher, Alexander Schnegg, Stephan Schulz, Stephan Barcikowski, Sven Reichenberger Chemcatchem, 2026 In this study, we employ the pulsed laser defect engineering in liquid (PUDEL) to tailor the surface properties of cobalt (II, III) oxide (Co 3 O 4 ) platelets grown in the < 111 > direction. By varying the laser intensity and pulse number, we systematically investigate the relationship between defect formation and catalytic performance in the oxygen evolution reaction (OER) and selective oxidation of two alcohols. Our results reveal that the PUDEL processing leads to the formation of lattice distortions, the gradual alteration of three different paramagnetic defect sites, a partial reduction of Co 3 O 4 , and enrichment of the Co 3 O 4 (111) surface with hydroxyl groups (*OH), which significantly enhances OER activity. Theoretical investigations confirm that optimized hydroxyl coverage is critical for determining OER activity. The observed trends in selectivity and conversion efficiency for the selective oxidation of cinnamyl alcohol (CA) and ethylene glycol (EG) suggest different reaction mechanisms. The activity trend of the selective oxidation of CA appears to follow the trend of a defect‐attributed paramagnetic species that was assigned to a surface‐near, distorted high‐spin (S = 3/2) Co 2+ . In turn, the catalytic activity and OER activity trends for the EG oxidation showed similar trends, which followed the density of a paramagnetic CoO x species observed during EPR spectroscopy. In particular, the highest OER activity and EG conversion were both found for moderate (2 PPV, ), yet not too intense PUDEL processing. Our findings establish PUDEL as a precise method for catalyst optimization, both for thermal and electro‐catalytic oxidation over defect‐enriched cobalt oxides, which enables the correlation of specific laser‐induced defects with catalytic activity trends.
Unifying Scaling Relations and Multiple Reaction Mechanisms for Screening Transition Metal-Doped Co3O4 for Oxygen Evolution Reaction Kapil Dhaka, Hatem M. A. Amin, Davide Beschi, Dana Schellenburg, Benjamin Mockenhaupt, Stephan Barcikowski, Stephan Schulz, Kai S. Exner Angewandte Chemie International Edition, 2026 Accelerating the discovery of oxygen‐evolution reaction (OER) catalysts requires high‐throughput screening strategies combining descriptor‐based frameworks with dedicated mechanistic analyses. In this study, we present a unified methodology using the example of doped Co 3 O 4 in the OER by developing a mechanistically resolved, potential‐dependent volcano approach that accounts for the uncertainty of adsorption free energies when analyzing activity trends. We evaluate the influence of different dopants (Cr, Mn, Fe, Ni, Cu, and V) on the OER activity by selectively substituting octahedral Co sites on the (001) facet of Co 3 O 4 using density functional theory calculations (DFT). We identify Cr, Fe, Ni, and V as promising dopants as they exhibit increased OER activity compared to undoped Co 3 O 4 , while Cr shows the strongest promoting effect among all dopants considered in this study. We compare our theoretical predictions with two different series of synthesized Co 3 O 4 nanoparticle catalysts and find good agreement regarding the qualitative trends of OER activity. To validate the strong promoting effect of Cr, we synthesize surface‐enriched, Cr‐doped Co 3 O 4 nanoparticles, which confirms the theoretical prediction of increased OER activity. The theoretical model developed in this work is a transferable framework that can be equally applied to other materials and electrocatalytic processes for quantifying dopant effects by considering uncertainty and promoting effects when analyzing activity trends.
Role of Fe decoration on the oxygen evolving state of Co3O4 nanocatalysts Felix T. Haase, Eduardo Ortega, Sascha Saddeler, Franz-Philipp Schmidt, Daniel Cruz, Fabian Scholten, Martina Rüscher, Andrea Martini, Hyo Sang Jeon, Antonia Herzog, Uta Hejral, Earl M. Davis, Janis Timoshenko, Axel Knop-Gericke, Thomas Lunkenbein, Stephan Schulz, Arno Bergmann, Beatriz Roldan Cuenya Energy and Environmental Science, 2024
Atomic layer deposition and characterization of Bi1Se1 thin films Shiyang He, Amin Bahrami, Xiang Zhang, Magdalena Ola Cichocka, Jun Yang, Jaroslav Charvot, Filip Bureš, Alla Heckel, Stephan Schulz, Kornelius Nielsch Journal of the European Ceramic Society, 2023
One-step synthesis of carbon-supported electrocatalysts Sebastian Tigges, Nicolas Wöhrl, Ivan Radev, Ulrich Hagemann, Markus Heidelmann, Thai Binh Nguyen, Stanislav Gorelkov, Stephan Schulz, Axel Lorke Beilstein Journal of Nanotechnology, 2020
Solid-state structure of bromine azide Benjamin Lyhs, Dieter Bläser, Christoph Wölper, Stephan Schulz, Georg Jansen Angewandte Chemie International Edition, 2012
Synthesis of tailor-made single source precursors for the deposition of binary group 13-antimonide thin films Proceedings Electrochemical Society, 2005
A single source approach for the deposition of GaSb films Proceedings Electrochemical Society, 2005
