Organic oxidation reactions (OORs) are emerging as attractive alternatives to the oxygen evolution reaction (OER) for renewable energy conversion. Effective OOR demands catalysts that function across diverse organic substrates and a broad chemical phase space. Here, we report a well-defined Ni12P5 nanostructure as an efficient alkaline OOR catalyst for 5-hydroxymethylfurfural (HMF) and 5-amino-1H-tetrazole (AmTET), yielding carboxylated and dehydrogenative N=N-coupled products, respectively. Dynamic redox behavior and self-reconstruction were investigated to identify the active phase. At OER potentials, Ni12P5 converts into NiIII/IV oxyhydroxides typical of OER catalysts. However, upon introducing organic substrates at catalytic potentials, the in situ formed NiIII/IVOOH is rapidly reduced, generating an OOR-active material dominated by NiII sites, as evidenced by quasi in situ X-ray absorption and in situ Raman spectroscopy. This work demonstrates the versatility and robustness of Ni-based electrocatalysts formed via potential-driven material transformations.

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.

Light-driven water splitting by plants, algae and cyanobacteria is pivotal for global bioenergetics and biomass formation. A manganese cluster bound to the photosystem II proteins catalyzes the complex reaction at high rate, but the rate-determining factors are insufficiently understood. Here we trace the oxygen-evolution transition by time-resolved polarography and infrared spectroscopy for cyanobacterial photosystems genetically modified at two strategic sites, complemented by computational chemistry. Our results highlight three rate-determining roles of the protein environment of the metal cluster: acceleration of proton-coupled electron transfer, acceleration of substrate-water insertion after O2-formation, and balancing of rate-determining enthalpic and entropic contributions. Whereas in general the substrate-water insertion step may be unresolvable in time-resolved experiments, here it likely becomes traceable because of deceleration by genetic modification. Our results may stimulate new time-resolved experiments on substrate-water insertion in photosynthesis, clarification of enthalpy-entropy compensation in enzyme catalysis, and knowledge-guided development of inorganic catalyst materials.

Water splitting is a promising pathway for hydrogen production, providing an environmentally friendly fuel source. More recently, great attention has been given to transition metal dichalcogenides (TMDCs) because of their interesting chemical and physical properties. In particular, tungsten disulfide (WS2) has garnered significant attention as a catalyst for this application due to its unique layered 2D structure. In this study, few-layered WS2 and phosphorus-doped WS2 (WS2/P) nanoflakes are synthesized on SiO2/Si substrates as electrocatalysts for hydrogen evolution reactions (HER) in acidic conditions. Analyses of the synthesized WS2 and WS2/P films reveal that the few-layered WS2 is of high quality, exhibiting continuity and uniformity. The presence of a strong peak in the photoluminescence spectrum confirms the mono/few layer nature of the synthesized samples. In additionally, scanning force microscopy in quantitative imaging mode reveals that the thinnest layers observed on the substrate have a height of 1.35 nm, indicating the presence of double-layer WS2. The WS2/P electrocatalyst demonstrates superior HER performance compared to pristine WS2, showing a low overpotential of 245 mV at 10 mA.cm−2 and a small Tafel slope of 123 mV.dec−1. Furthermore, WS2/P exhibits a greater electrochemical surface area and excellent catalytic stability under acidic conditions. Consequently, few layer phosphorus-doped WS2 proves to be a highly suitable electrocatalyst for hydrogen production compared to the WS2.

A dinuclear copper(I) complex Cu2L22 (L2 = 3,3-dimethyl-1-(1-methyl-1H-benzo[d]imidazole-2-yl)-N-(propan-2-ylidene)butan-2-amine) containing benzimidazole and imino donors was previously reported by some of us as an efficient catalyst for the aerobic oxidation of alcohols to aldehydes in presence of TEMPO (2,2,6,6-tetramethylpiperidinyloxyl) and an external base NMI (N-methyl imidazole). Cu(III)2(bis-μ-oxo) and Cu(II)2(bis-μ-hydroxo) cores were trapped as viable intermediates in the reaction, which provided deeper mechanistic insights. Here, we report two new ligand systems L3 (N-isopropyl-3,3-dimethyl-1-(1-methyl-1H-benzol[d]imidazole-2-yl)butane-2-amine) and L4 ((Z)-2,4-di-tert-butyl-6-(((3,3-dimethyl-1-(1-methyl-1H-benzol[d]imidazole-2-yl)butane-2-yl)imino)methyl)phenol), which are designed to perturb the overall electronics of the complexes and the resulting effects on their O2 activation mechanisms. The stronger donation of the secondary amine group stabilizes a mononuclear CuIL3 core, which nevertheless follows a dinuclear O2 activation mechanism as in Cu2L22. Notably, the CuIL3/TEMPO catalyst system performs the aerobic oxidation of alcohols to aldehydes with good yields and turnover numbers, even in the absence of NMI. The dinuclear CuI 2L42 complex involving a non-innocent phenolate group, in contrast, exhibits depleted catalytic activity, because of the instability of the Cu(III)2(bis-μ-oxo) core against intramolecular H-atom abstraction to form an alkoxo bridged dicopper(II) complex.

Developing low-cost, highly active, and stable catalysts for the acidic oxygen evolution reaction (OER) at the proton exchange membrane (PEM) water electrolyzer anodes remains a scientific priority. Reducing the iridium loading while increasing the intrinsic activity of the catalysts is essential for cost-effective hydrogen production. Here, we address a family of TiO2-supported Raney-IrO x catalysts with low iridium loading and high activity in single-cell PEM water electrolyzer anode environments. A controlled Raney-type Ni leaching process of pristine, supported IrNi alloy phases forms crystalline IrO x nanoparticles (NPs) featuring metallic Ir-rich cores surrounded by more amorphous IrO x surfaces. This structure is shown to be conducive to catalytic activity and the suppression of membrane poisoning due to Ni degradation. The trace amounts of Ni remaining after leaching in the IrO x NPs result in heterogeneous crystal structure and induce local lattice strain. Further, we synthetically strike a balance between conductivity and activity and succeed to narrow down the notorious large performance gap between liquid electrolyte rotating disk electrodes (RDEs) and single-cell membrane electrode assembly (MEA) electrolyzer measurements. OER stability numbers (S-numbers) of the identified Raney-IrO x anode catalysts surpass commercial IrO2 catalysts, confirming the stability of these catalysts. The PEM electrolyzer tests reveal that Raney-IrO x anodes achieve 3 A cm-2 at 1.8 V with a low geometric Ir loading of ca. 0.3 mgIr cm-2, meeting the technically important power specific Ir utilization target of 0.05 gIr/kW.

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.

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.

The diiron(II) complex, [(OCO)Fe(MeCN)](2) (1, MeCN = acetonitrile), supported by the bis-phenolate carbene pincer ligand, 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)benzimidazolin-2-ylidene (OCO), was synthesized and characterized by single-crystal X-ray diffraction,H- 1 nuclear magnetic resonance, infrared (IR) vibrational, ultraviolet/visible/near-infrared (UV/vis/NIR) electronic absorption, Fe-57 Mossbauer, X-band electron paramagnetic resonance (EPR) and SQUID magnetization measurements. Complex 1 activates dioxygen to yield the diferric, mu-oxo-bridged complex [(OCO)Fe(py)(mu-O)Fe(O(C=O)O)(py)] (2) that was isolated and fully characterized. In 2, one of the iron-carbene bonds was oxidized to give a urea motif, resulting in an O(C-NHC equivalent to O)O binding site, while the other Fe(OCO) unit remained unchanged. When the reaction is performed at -80 degrees C, an intensively colored, purple intermediate is observed (INT, lambda(max) = 570 nm; epsilon = 5600 mol L-1 cm(-1)). INT acts as a sluggish oxidant, reacting only with easily oxidizable substrates, such as PPh3 or 2-phenylpropionic aldehyde (2-PPA). The identity of INT can be best described as a dinuclear complex containing a closed diamond core motif [(OCO)Fe-IV(mu-O)(2)Fe-IV(OCO)]. This proposal is based on extensive spectroscopic [UV/vis/NIR electronic absorption, Fe-57 Mossbauer, X-band EPR, resonance Raman (rRaman), X-ray absorption, and nuclear resonance vibrational (NRVS)] and computational studies. The conversion of the diiron(II) complex 1 to the oxo diiron(IV) intermediate INT is reminiscent of the O-2 activation process in soluble methane monooxygenases (sMMO). Most importantly, the low reactivity of INT supports the consensus that the [Fe-IV(mu-O)(2)Fe-IV] diamond core in sMMO is kinetically inert and needs to open up to terminal Fe-IV=O cores to react with the strong C-H bonds of methane.

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

Cytochrome c oxidase (CcO) is a heme−copper oxidase (HCO) that catalyzes the natural reduction of oxygen to water. A pro-found understanding of some of the elementary steps leading to the intricate 4e−/4H+ reduction of O2 is presently lacking. A St = 1 FeIII−(O22−)−CuII (IP) intermediate is proposed to reduce the overpotentials associated with the reductive O−O bond rupture by allowing electron transfer from a tyrosine moiety without the necessity of any spin-surface crossing. Direct evidence of the in-volvement of IP in the HCO catalytic cycle is, however, missing. A number of heme-copper peroxido complexes have been pre-pared as synthetic models of IP; but all of them possess the catalytically non-relevant St = 0 ground state resulting from antiferro-magnetic coupling between the S = 1/2 FeIII and CuII centers. In a complete non-heme approach, we now report the spectroscopic characterization and reactivity of the FeIII−(O22−)−CuII intermediates 1 and 2, which differ only by a single −CH3 versus −H sub-stituent on the central amine of the tridentate ligands binding to copper. Complex 1 with an end-on peroxido core, and ferromag-netically (St=1) coupled FeIII and CuII centers performs H-bonding mediated O−O bond cleavage in presence of phenol to generate oxoiron(IV), copper(II) and PhO•. In contrast, the side-on peroxide complex 2, with a St = 0 ground-state is unreactive towards phenol. Thus, the implications for spin topology contributions to O−O bond cleavage, as proposed for the heme FeIII−(O22−)−CuII intermediate in CcO, can be extended to non-heme chemistry.

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.

Transition-metal nanoparticles hold great promise as electrocatalysts for alkaline hydrogen evolution reaction (HER), however, addressing the simultaneous challenges of ensuring sufficient active sites, promoting favorable water dissociation, and optimizing binding energy toward hydrogen intermediates remains a formidable task. To overcome these hurdles, a novel gaseous hydrogen engineering strategy is proposed by in situ embedding cobalt nanoparticles within a samarium hydride matrix (Co/SmH2) via hydrogen-induced disproportionation of SmCo5 particles for efficient alkaline HER. The as-designed Co/SmH2 delivered an overpotential as low as 252 mV at 100 mA cm-2, surpassing the performance of pristine Co by 100 mV. Notably, this catalyst lasts remarkably long maintaining a durability at approximate to 500 mA cm-2 for 120 h. A combination of in situ Raman spectroscopy, in situ X-ray absorption spectroscopy, density functional theory calculation and post-HER characterizations unambiguously unveiled that the surface SmH2 transforms into samarium (hydr)oxide during electrocatalysis. This transformation not only inhibits the aggregation of the ultrafine cobalt nanoparticles but also significantly enhances the water dissociation and optimizes the binding energy of active cobalt species toward hydrogen intermediate, resulting in concurrent improvement of kinetics, thermodynamics, and stability of the HER process. Hydrogen-induced disproportionation of SmCo5 facilitates the uniform confinement of nanoscopic cobalt by SmH2 nanocrystals, which turns out to be cooperative and highly active, and durable in alkaline hydrogen evolution reaction (HER). The conversion of surface SmH2 to samarium (hydr)oxide during catalysis plays a pivotal role in achieving optimized structural stability, water dissociation kinetics, and adsorption-free energy toward the *H intermediate. image

Recently, Ni molecular catalysis has been extensively applied in oxygenation reactions. This work is underpinned by the characterization techniques and the discovered instability of the Ni-bipyridine/phenanthroline system, which results in Ni (hydr)oxide production under oxidative conditions. The practical applications of this mechanism by employing a prepared Ni (hydr)oxide-based electrode specifically in the oxygenation of sulfides, achieving noteworthy yields in contrast to noncatalyst control experiments, are explored. Thus, a Ni (hydr)oxide-based material is proposed as a candidate for the true catalyst for sulfide oxidation in the presence of the Ni-bipyridine/phenanthroline system. The findings of this study are expected to stimulate discussion and encourage new viewpoints within the chemical community regarding the potential applications and mechanisms of molecular catalysts in oxidation reactions.

Developing Mn-based water-oxidation reaction (WOR) catalysts is key for renewable energy storage, utilizing Mn's abundance, cost-effectiveness, and natural role. Cerium(IV) ammonium nitrate (CAN) has been widely utilized as a sacrificial oxidant in the exploration of WOR catalysts. In this study, advanced techniques, such as X-ray absorption spectroscopy (XAS), in situ Raman spectroscopy, and in situ electron paramagnetic resonance (EPR), to delve into the WOR facilitated by CAN and birnessite were employed. XANES analysis has demonstrated that the average oxidation states (AOSs) of Mn in birnessite, a birnessite/CAN mixture, and in the birnessite/CAN mixture postwater addition are 3.7, 3.8, and 3.9, respectively. In situ Raman spectroscopy performed in the presence of birnessite and CAN revealed a distinct peak at 784 cm-1, which is attributed to Mn(IV)=O. A shift of this peak to 769 cm-1 in H2 18O confirms its association with Mn(IV)=O. No change in this peak was observed in D2O, further supporting the notion that it is linked to Mn(IV)=O rather than Mn-OH (D). Furthermore, EPR spectroscopy shows the presence of Mn(IV). It is suggested that the WOR mechanism initiates with the oxidation of birnessite by CAN, which enhances the concentration of Mn(IV) sites in the birnessite structure. Under acidic conditions, birnessite, enriched in Mn(IV), facilitates oxygen evolution and subsequently transitions into a form with reduced Mn(IV) levels. This process highlights the critical function of the Mn (hydr)oxide structure, similar to its role in the water-oxidizing complex of Photosystem II, where it serves as charge storage for oxidizing equivalents from CAN, paving the way for a four-electron reaction that drives the WOR.

Water oxidation, the oxygen evolution reaction (OER), is the anodic process in electrocatalytic production of hydrogen and further green fuels. Transition-metal oxyhydroxides with bulk-phase OER activity of the complete material or amorphized near-surface regions are of prime application interest, but their basic electrochemical properties are insufficiently understood. Here the timescale of functional processes is clarified by time-resolved X-ray absorption spectroscopy and electrochemical impedance spectroscopy (EIS) for a thickness-series of cobalt oxyhydroxides films (about 35-550 nm). At the outer material surface, an electric double-layer is formed in microseconds followed by clearly cobalt-centered redox-state changes of the bulk material in the low millisecond domain and a slow chemical step of O2-formation, within hundreds of milliseconds. Conceptually interesting, the electrode potential likely controls the OER rate indirectly by driving the catalyst material to an increasingly oxidized state which promotes the rate-limiting chemical step. Rate constants are derived for redox chemistry and catalysis from EIS data of low-thickness catalyst films; at higher thicknesses, catalyst-internal charge transport limitations become increasingly relevant. Relations between electrochemically active surface area, double-layer capacitance, and redox (pseudo-)capacitance are discussed. These results can increase the power of EIS analyses and support knowledge-guided optimization of a broader class of OER catalyst materials.

Cytochrome c oxidase (CcO) is a heme copper oxidase (HCO) that catalyzes the natural reduction of oxygen to water. A profound understanding of some of the elementary steps leading to the intricate 4e(-)/4H(+) reduction of O-2 is presently lacking. A total spin S-t = 1 Fe-III-(O-2(2-))-Cu-II (I-P) intermediate is proposed to reduce the overpotentials associated with the reductive O-O bond rupture by allowing electron transfer from a tyrosine moiety without the necessity of any spin-surface crossing. Direct evidence of the involvement of I-P in the CcO catalytic cycle is, however, missing. A number of heme copper peroxido complexes have been prepared as synthetic models of I-P, but all of them possess the catalytically nonrelevant S-t = 0 ground state resulting from antiferromagnetic coupling between the S = 1/2 Fe-III and Cu-II centers. In a complete nonheme approach, we now report the spectroscopic characterization and reactivity of the Fe-III-(O-2(2-))-Cu-II intermediates 1 and 2, which differ only by a single -CH3 versus -H substituent on the central amine of the tridentate ligands binding to copper. Complex 1 with an end-on peroxido core and ferromagnetically (S-t = 1) coupled Fe-III and Cu-II centers performs H-bonding-mediated O-O bond cleavage in the presence of phenol to generate oxoiron(IV) and exchange-coupled copper(II) and PhO center dot moieties. In contrast, the mu-eta(2):eta(1) peroxido complex 2, with a S-t = 0 ground state, is unreactive toward phenol. Thus, the implications for spin topology contributions to O-O bond cleavage, as proposed for the heme Fe-III-(O-2(2-))-Cu-II intermediate in CcO, can be extended to nonheme chemistry.

The development of catalysts for an economical and efficient oxygen evolution reaction (OER) is critical for clean and sustainable energy storage and conversion. Nickel-iron-based (NiFe) nanostructures are widely investigated as active OER catalysts and especially shape-controlled nanocrystals exhibit optimized surface structure and electronic properties. However, the structural control from amorphous to well-defined crystals is usually time-consuming and requires multiple stages. Here, a universal two-step precipitation-hydrothermal approach is reported to prepare a series of NiFe-based nanocrystals (e.g., hydroxides, sulfides, and molybdates) from amorphous precipitates. Their morphology and evolution of atomic and electronic structure during this process are studied using conclusive microscopy and spectroscopy techniques. The short-term, additive-free, and low-cost method allows for the control of the crystallinity of the materials and facilitates the generation of nanosheets, nanorods, or nano-octahedra with excellent water oxidation activity. The NiFe-based crystalline catalysts exhibit slightly compromised initial activity but more robust long-term stability than their amorphous counterparts during electrochemical operation. This facile, reliable, and universal synthesis method is promising in strategies for fabricating NiFe-based nanostructures as efficient and economically valuable OER electrocatalysts.

Oxide-derived copper (OD-Cu) materials exhibit extraordinary catalytic activities in the electrochemical carbon dioxide reduction reaction (CO2RR), which likely relates to non-metallic material constituents formed in transitions between the oxidized and the reduced material. In time-resolved operando experiment, we track the structural dynamics of copper oxide reduction and its re-formation separately in the bulk of the catalyst material and at its surface using X-ray absorption spectroscopy and surface-enhanced Raman spectroscopy. Surface-species transformations progress within seconds whereas the subsurface (bulk) processes unfold within minutes. Evidence is presented that electroreduction of OD-Cu foams results in kinetic trapping of subsurface (bulk) oxide species, especially for cycling between strongly oxidizing and reducing potentials. Specific reduction-oxidation protocols may optimize formation of bulk-oxide species and thereby catalytic properties. Together with the Raman-detected surface-adsorbed *OH and C-containing species, the oxide species could collectively facilitate *CO adsorption, resulting an enhanced selectivity towards valuable C2+ products during CO2RR.

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.