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Producing hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. With spin-dependent kinetics in OER, to manipulate the spin ordering of ferromagnetic OER catalysts (e.g., by magnetization) can reduce the kinetic barrier. However, most active OER catalysts are not ferromagnetic, which makes the spin manipulation challenging. In this work, we report a strategy with spin pinning effect to make the spins in paramagnetic oxyhydroxides more aligned for higher intrinsic OER activity. The spin pinning effect is established in oxideFM/oxyhydroxide interface which is realized by a controlled surface reconstruction of ferromagnetic oxides. Under spin pinning, simple magnetization further increases the spin alignment and thus the OER activity, which validates the spin effect in rate-limiting OER step. The spin polarization in OER highly relies on oxyl radicals (O∙) created by 1st dehydrogenation to reduce the barrier for subsequent O-O coupling., Water oxidation to triplet oxygen requires a spin polarization process for faster kinetics. Here, the authors show an interface spin pinning effect between ferromagnetic oxides and reconstructed oxyhydroxide surface layer, where the spin ordering in paramagnetic oxyhydroxide catalyst layer can be tuned to improve the intrinsic activity.

Thorough analyses of structural factors in catalysis are interesting because they allow the massive prescreening of potential optimum compositions. Overall, this article shows how the orbital physics of magnetic compositions relates with spin–lattice interactions and then band gaps and bond lengths together become relevant descriptors in catalytic oxygen technologies. Active electrocatalysts for the oxygen evolution reaction (OER) include magnetic oxides with metals at relatively high oxidation states, so chemisorbed molecular O2 is not very stable. On the other hand, ideal compositions for the oxygen reduction reaction (ORR) have metals in a comparatively lower oxidation state, which can supply electrons to activate O2 molecules toward electron-richer oxygen atoms. Spin–lattice interactions in these strongly correlated oxides relate the orbital configurations and oxidation state with distinctive metal–oxygen bond distances, indicating localized or itinerant electronic behavior and selectivity in oxygen e...

The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons’ transfer and the generation of triplet state O2 from singlet state species (OH- or H2O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O2. Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts., Here, authors demonstrate the ferromagnetic catalyst to facilitate spin polarization in water oxidation reaction. They find the ferromagnetic-exchange-like behaviour between the ferromagnetic catalyst and the adsorbed oxygen species.

Oxygen evolution and reduction reactions play a critical role in determining the efficiency of the water cycling (H2O ⇔ H2 + 1/2O2), in which the hydrogen serves as the energy carrier. That calls for a comprehensive understanding of oxygen electrocatalysis for efficient catalyst design. Current opinions on oxygen electrocatalysis have been focused on the thermodynamics of the reactant/intermediate adsorption on the catalysts. Because the oxygen molecule is paramagnetic, its production from or its reduction to diamagnetic hydroxide/water involves spin-related electron transfer. Both electron transfer and orbital interactions between the catalyst and the reactant/intermediate show spin-dependent character, making the reaction kinetics and thermodynamics sensitive to the spin configurations. Herein, a brief introduction on the spintronic explanation of the catalytic phenomena on oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is given. The local spin configurations and orbital interactions in the benchmark transition-metalbased catalysts for OER and ORR are analyzed as examples. To further understand the spintronic oxygen electrocatalysis and to develop more efficient spintronic catalysts, the challenges are summarized and future opportunities proposed. Spin electrocatalysis may emerge as an important topic in the near future and help integrate a comprehensive understanding of oxygen electrocatalysis. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work was supported by Singapore Ministry of Education Tier 2 Grant (MOE- 2018-T2-2-027).

Electrons in covalent oxides are fermions interacting through overlapping atomic orbitals, and quantum exchange interactions incorporate influential spin-dependent potentials in their electrocatalytic properties. The Goodenough-Kanamori rules explain the magnetic coupling between metals connected via ligands, known as super- (or double-) exchange interactions, which regulate their charge transport properties. To describe the electrocatalytic activity of magnetic metal oxides, we must extend their spin-dependent mechanisms of electron tunnelling to catalytic interfaces, because the exchange coupling between orbitals, in the catalysts and with the chemisorbed reactants, influences the kinetics of electron transfer reactions. The principles for developing magnetic coupling rules in electrocatalysis must guarantee spin passages, which are optimum for intrinsically degenerate configurations of the frontier orbitals oriented in the direction of the bonds at both sides of the Fermi level. A continuous energy landscape between the reactants and the catalyst minimizes the overpotentials during coherent redox electron tunnelling. Consequently, in this paper we derive the guidelines of the ferromagnetic (FM) exchange interactions, an extension of the Goodenough-Kanamori rules, to electrocatalytic interfaces, which anticipates minimum Gibbs energy of activation. We focus on the electronic coordinates, targeting reaction conditions where the electrons are the main energy carriers to trigger the steps; nonetheless they are inter-related with the atomic movements. We will use the oxygen evolution and reduction reactions as examples where quantum exchange interactions, a landmark of solid-state magnetism, and the chemistry of the triplet state O 2 molecule, are crucial for optimum kinetics. One sentence summary: Delocalizing spin potentials facilitate the coherent propagation of electrons at covalent magnetic interfaces; this is a physical principle that links ferromagnetic exchange interactions, antibonding orbitals and optimum viable electrocatalysis: spintro-catalysis.

The study of magnetic perovskite oxides has led to novel and very active compounds for O2 generation and other energy applications. Focusing on three different case studies, we summarise the bulk electronic and magnetic properties that initially serve to classify active perovskite catalysts for the oxygen evolution reaction (OER). Ab-initio calculations centred on the orbital physics of the electrons in the d-shell provide a unique insight into the complex interplay between spin dependent interactions versus selectivity and OER reactivity that occurs in these transition-metal oxides. We analyse how the spin, orbital and lattice degrees of freedom establish rational design principles for OER. We observe that itinerant magnetism serves as an indicator for highly active oxygen electro-catalysts. Optimum active sites individually have a net magnetic moment, giving rise to exchange interactions which are collectively ferromagnetic, indicative of spin dependent transport. In particular, optimum active sites for OER need to possess sufficient empty orthogonal orbitals, oriented towards the ligands, to preserve an incoming spin aligned electron flow. Calculations from first principles open up the possibility of anticipating materials with improved electro-catalytic properties, based on orbital engineering.

The orbital physics relevant in electrocatalytic activity present subtle differencies between oxygen evolution (OER) and reduction reactions (ORR). Achieving maximum efficiency in (electro)catalysis requires a detailed understanding on the electronic interactions. Quantum correlations and, in particular, spin-exchange interactions are decisive to understand the necessary underlying physics. Besides adsorption energies of reaction intermediates, there are other critical factors to characterize electrocatalysts such as charge, spin and flow sense of the electron transport. A revolution is going on right now in the understanding of oxygen electrochemistry, meant to close the gap with the novel research in strongly correlated materials or spintronics and to re-establish general fundaments of catalysis. We present a concise review taking as central example the dual catalyst LaNi0.8Fe0.2O3.

The oxygen evolution complex (OEC) of photosystem II (PSII) is intrinsically more active than any synthetic alternative for the oxygen evolution reaction (OER). A crucial question to solve for the progress of artificial photosynthesis is to understand the influential interactions during water oxidation in PSII. We study the principles of interatomic electron transfer steps in OER, with emphasis on exchange interactions, revealing the influence of delocalizing ferromagnetic spin potentials during the catalytic process. The OEC is found to be an exchange coupled mixed-valence electron-spin acceptor where its orbital physics determine the unique activity of PSII. The two unpaired electrons needed in the triplet O2 molecule interact with the high spin state of the catalyst via exchange interactions; the optimal ferromagnetic catalyst and the resulting radical intermediates are spin paired. As a result, the active center of the CaMn4O5 cofactor, stimulated by the driving potential provided by photons, works as...

Manganese oxides with a half-metallic ground state are particularly active for oxygen reduction reactions (ORR). La0.67Sr0.33MnO3 (LSMO) perovskite is the archetypal example for compositions with a Curie temperature (TC) above room temperature, and with a high intrinsic activity for the partial reduction of triplet state O2. The ferromagnetic (FM) character of the superexchange interactions in LSMO facilitates both the charge and spin transport below 370 K. Other than the enhanced electronic conductivity, the reduced spin entropy seems to be of relevance in oxygen catalysis, as the magnetic ordering extends to the surface. The sign of the exchange interactions determines the adsorption of the triplet oxygen molecule with its spin antiparallel to the FM catalysts. On the basis of transition state theory, we report that on LSMO the hindrance due to the magnetic entropy for the initial reduction of O2 by two antiparallel electrons to diamagnetic intermediates (like H2O2) is minimum. On the other hand, the additional reduction of H2O2 to H2O, diamagnetic steps, prefers paramagnetic catalysts, with higher magnetic entropy like La0.4Sr0.6MnO3, to avoid spin accumulation.

Water electrolysis is the most promising method for efficient production of high purity hydrogen (and oxygen), while the required power input for the electrolysis process can be provided by renewable sources (e.g. solar or wind). The thus produced hydrogen can be used either directly as a fuel or as a reducing agent in chemical processes, such as in Fischer–Tropsch synthesis. Water splitting can be realized both at low temperatures (typically below 100 °C) and at high temperatures (steam water electrolysis at 500–1000 °C), while different ionic agents can be electrochemically transferred during the electrolysis process (OH−, H+, O2−). Singular requirements apply in each of the electrolysis technologies (alkaline, polymer electrolyte membrane and solid oxide electrolysis) for ensuring high electrocatalytic activity and long-term stability. The aim of the present article is to provide a brief overview on the effect of the nature and structure of the catalyst–electrode materials on the electrolyzer's performance. Past findings and recent progress in the development of efficient anode and cathode materials appropriate for large-scale water electrolysis are presented. The current trends, limitations and perspectives for future developments are summarized for the diverse electrolysis technologies of water splitting, while the case of CO2/H2O co-electrolysis (for synthesis gas production) is also discussed.

Reactions involving nitrogen fixation and transfer are of great industrial interest. In this regard, unveiling all the physical principles that determine their activity would be enormously beneficial for the rational design of novel catalysts with improved performance. Within this context, this work explores the activity of bulk molybdenum-based transition metal nitrides in ammonia synthesis. Our results highlight that the most active compositions show increasing ferromagnetism in the metal-nitrogen bonds, which constitute the active sites. We observe that the total spin accumulated in the bonds at the active sites is a physically meaningful descriptor to discriminate optimum catalysts. Higher activities are associated with ferromagnetic phases, and the underlying reason is an enhanced overlapping of the electronic wavefunctions; which also make the reaction steps spin-sensitive. These finding provides strong evidence of the general influence of electrons magnetic moment in catalysis, being part of the specific field of spintro-catalysis.

The definition of the interplay between chemical composition, electro-magnetic configuration and catalytic activity requires a rational study of the orbital physics behind active materials. Apart from Coulomb forces, quantum spin exchange interactions (QSEI) are part of the potentials that differentiate the activity of magnetic oxides, strongly correlated electrocatalysts, in electron transfer reactions. Ferromagnetic (FM) cobalt oxides can show low overpotentials for the oxygen evolution reaction (OER) and the La1XSrXCoO3d (0 r X r 1) family of perovskites is good ground to gain understanding of the electronic interactions in strongly correlated catalysts. In this case, Sr-doping raises the OER activity and the conductivity and increases FM spin moments. The efficiency of electrocatalysts based on Earth-abundant 3d-transition metals correlates with the interrelated factors: mild-bonding energies, the reduction of the electronic repulsions because of the QSEI in the open-shells, and enhanced spin delocalization in FM ordering. The reason for the outstanding OER activity of SrCoO3d is the accumulation of FM holes in the 3d–2p bonds, including the ligand orbitals, thus facilitating spinselected charge transport and production of triplet O2 moieties from the oxidation of diamagnetic precursors. Spin-polarized oxygen atoms in the lattice can participate in O–O coupling and release of O2 in a Mars–Van Krevelen mechanistic fashion. We show that the stabilizing FM QSEI decrease the adsorption and activation energies during oxygen evolution and spin-dependent potentials are one of the factors that govern the catalytic activity of magnetic compositions: spintro-catalysis.

We have performed an in-depth ab initio study of the magnetic structure within the most active perovskites for the oxygen evolution reaction. In all cases, the ground state exhibits an extended antiferromagnetic coupling in the unit cell. Layered antiparallel alignment of the magnetic moments appears to be related to their electrocatalytic activity. All the perovskites calculated within this paper show space-separated charge-transport channels depending on the spin orientation. Comparing the electronic structures with the reported activities, we find a direct correlation between the magnetic accumulation on the spin channels in the bulk material and the catalytic activity. We discuss the possible implications of such observations in terms of magnetic interactions. During oxygen evolution in water electrolysis, reactants and products do not preserve spin. For triplet state oxygen to evolve, the catalyst at the anode can speed up the reaction if it is able to balance the magnetism of the oxygen molecule by extracting electrons with an opposite magnetic moment, conserving the overall spin.

The spin of the electron is decisive to understand electronic interactions in heterogeneous catalysis, mainly because the stabilizing Quantum Spin Exchange Interactions (QSEI) are always a significant contribution to the energy of magnetic catalysts and absorbates during reaction events. Cooperative QSEI in compositions with multi-atomic open-shell configurations (QSEI-OS) maximize the influence of the spin dependent potentials, determining the electronic properties of magnetic materials and shaping their reactivity. In this paper, we explain that because of the intra- and inter- atomic QSEI-OS, high-spin (3d5) antiferromagnetic (AFM) metals like Cr and Mn can be more inert (or “noble”) than Au itself towards the formation of covalent bonds with hydrogen atoms. AFM QSEI-OS lead to a relative higher destabilization of the unoccupied (spin-)orbitals (Mott upper band) in Cr and Mn compared with other metals. In oxygen adsorption, QSEI-OS lead to the reduction of the electronic repulsions in occupied 3d5 orbitals with a concomitant decrease of the chemisorption enthalpy of the oxygen atoms. Since hydrogen and oxygen atoms are the most important intermediates in relevant catalytic processes like oxygen reduction reaction and water splitting, we observe how the effect of QSEI-OS needs to be properly incorporated as a critical factor to understand the activity of catalysts based on magnetic metals.

The technological interest of oxygen reduction and evolution reactions, ORR and OER, for the clean use and storage of energy has resulted in the discovery of multiple catalysts; and the physical and catalytic properties of the most active compositions are only comprehensible with the consideration of magnetic interactions. Spin dependent potentials via exchange interactions, spin-orbit coupling or through magneto-electric effects catalyse the oxygen electrochemistry. The best catalysts show metal sites with localized spins and electron delocalization; a correlation exists between the rate constant for charge transfer reactions and spin-dependent electron mobility. Since during the OER and ORR the number of unpaired electrons is not conserved, magnetic potentials in optimum catalysts act as selective gates to enhance the transport of local spin currents. Overall magnetic potentials can reduce the bonding properties of the, donor or acceptor, orbitals in the catalyst, and electrons more easily transfer over the conduction band. The influence of spin dependent forces is generally applicable to oxygen catalysis, and supplements the physical interactions relevant for inorganic or organic, electro or photo, artificial or natural processes.

This study investigates the production of hydrogen from the electrochemical reforming of short-chain alcohols (methanol, ethanol, iso-propanol) and their mixtures. High surface gas diffusion Pt/C electrodes were interfaced to a Nafion polymeric membrane. The assembly separated the two chambers of an electrochemical reactor, which were filled with anolyte (alcohol�+�H2O or alcohol�+�H2SO4) and catholyte (H2SO4) aqueous solutions. The half-reactions, which take place upon polarization, are the alcohol electrooxidation and the hydrogen evolution reaction at the anode and cathode, respectively. A standard Ag/AgCl reference electrode was introduced for monitoring the individual anodic and cathodic overpotentials. Our results show that roughly 75% of the total potential losses are due to sluggish kinetics of the alcohol electrooxidation reaction. Anodic overpotential becomes larger as the number of C-atoms in the alcohol increases, while a slight dependence on the pH was observed upon changing the acidity of the anolyte solution. In the case of alcohol mixtures, it is the largest alcohol that dictates the overall cell performance.

Stable, alkyl-terminated, light-emitting silicon nanoparticles have been synthesized in a continuous process by laser pyrolysis of a liquid trialkyl-silane precursor selected as a safer alternative to gas silane (SiH4). Stabilization was achieved by in situ reaction using a liquid collection system instead of the usual solid state filtration. The alkene contained in the collection liquid (1-dodecene) reacted with the newly formed silicon nanoparticles in an unusual room-temperature hydrosilylation process. It was achieved by the presence of fluoride species, also produced during laser pyrolysis from the decomposition of sulfur hexafluoride (SF6) selected as a laser sensitizer. This process directly rendered alkyl-passivated silicon nanoparticles with consistent morphology and size (

We analyze the temperature increase in Linde Type A Na, K, and Ca mix zeolites under microwave radiation. Through the use of the density functional theory (DFT), we examine the movements of the most labile cations for dehydrated Na12, K12, and Na4Ca4 ideal A-zeolites. The kinetics of the ionic migration, responsible for dielectric heating, is described according to transition-state theory. For each composition, we find different relaxation processes caused by the jump of the most unbalanced cations to diverse metastable sites inside the Al–O–Si framework. The magnitudes of the calculated enthalpy barriers for the most probable jumps agree with the experiments and are inversely related to the heating rates. DFT calculations are an optimum approach to elucidate the cation migration in Zeolites, described by a thermally activated or Arrhenius-type process. We observe that the deposition of microwave energy drops significantly in the presence of Ca atoms independently of other cations.