A catalyst functions by stabilizing reaction intermediates, usually through surface adsorption. In the oxygen evolution reaction (OER), surface oxygen adsorption plays an indispensable role in the electrocatalysis. The relationship between the adsorption energetics and OER kinetics, however, has not yet been experimentally measured. Herein we report an experimental relationship between the adsorption of surface oxygen and the kinetics of the OER on IrO(110) epitaxially grown on a TiO(110) single crystal. The high quality of the IrO film grown using molecular-beam epitaxy affords the ability to extract the surface oxygen adsorption and its impact on the OER. By examining a series of electrolytes, we find that the adsorption energy changes linearly with pH, which we attribute to the electrified interfacial water. We support this hypothesis by showing that an electrolyte salt modification can lead to an adsorption energy shift. The dependence of the adsorption energy on pH has implications for the OER kinetics, but it is not the only factor; the dependence of the OER electrocatalysis on pH stipulates two OER mechanisms, one operating in acidic solution and another operating in alkaline solution. Our work points to the subtle adsorption-kinetics relationship in the OER and highlights the importance of the interfacial electrified interaction in electrocatalyst design.

The well-known frameworks of the type M2(dobdc) (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate) have numerous potential applications in gas storage and separations, owing to their exceptionally high concentration of coordinatively unsaturated metal surface sites, which can interact strongly with small gas molecules such as H2. Employing a related meta-functionalized linker that is readily obtained from resorcinol, we now report a family of structural isomers of this framework, M2(m-dobdc) (M = Mg, Mn, Fe, Co, Ni; m-dobdc(4-) = 4,6-dioxido-1,3-benzenedicarboxylate), featuring exposed M(2+) cation sites with a higher apparent charge density. The regioisomeric linker alters the symmetry of the ligand field at the metal sites, leading to increases of 0.4-1.5 kJ/mol in the H2 binding enthalpies relative to M2(dobdc). A variety of techniques, including powder X-ray and neutron diffraction, inelastic neutron scattering, infrared spectroscopy, and first-principles electronic structure calculations, are applied in elucidating how these subtle structural and electronic differences give rise to such increases. Importantly, similar enhancements can be anticipated for the gas storage and separation properties of this new family of robust and potentially inexpensive metal-organic frameworks.

The use of renewable electricity to prepare materials and fuels from abundant molecules offers a tantalizing opportunity to address concerns over energy and materials sustainability. The oxygen evolution reaction (OER) is integral to nearly all material and fuel electrosyntheses. However, very little is known about the structural evolution of the OER electrocatalyst, especially the amorphous layer that forms from the crystalline structure. Here, we investigate the interfacial transformation of the SrIrO3 OER electrocatalyst. The SrIrO3 amorphization is initiated by the lattice oxygen redox, a step that allows Sr2+ to diffuse and O2− to reorganize the SrIrO3 structure. This activation turns SrIrO3 into a highly disordered Ir octahedral network with Ir square-planar motif. The final SryIrOx exhibits a greater degree of disorder than IrOx made from other processing methods. Our results demonstrate that the structural reorganization facilitated by coupled ionic diffusions is essential to the disordered structure of the SrIrO3 electrocatalyst.

Superconductivity is among the most fascinating and well-studied quantum states of matter. Despite over 100 years of research, a detailed understanding of how features of the normal-state electronic structure determine superconducting properties has remained elusive. For instance, the ability to deterministically enhance the superconducting transition temperature by design, rather than by serendipity, has been a long sought-after goal in condensed matter physics and materials science, but achieving this objective may require new tools, techniques and approaches. Here, we report the transmutation of a normal metal into a superconductor through the application of epitaxial strain. We demonstrate that synthesizing RuO2 thin films on (110)-oriented TiO2 substrates enhances the density of states near the Fermi level, which stabilizes superconductivity under strain, and suggests that a promising strategy to create new transition-metal superconductors is to apply judiciously chosen anisotropic strains that redistribute carriers within the low-energy manifold of d orbitals.

Chlorine evolution reaction electrocatalysis on RuO 2 (110) and IrO 2 (110) grown using molecularbeam epitaxy

Understanding how physicochemical properties of materials affect the oxygen evolution reaction (OER) has enormous scientific and technological implications for the OER electrocatalyst design. We present our investigation on the role of strain on the surface–oxygen interaction and the OER on well-defined single-termination SrIrO3 films. Our approach employs a combination of molecular-beam epitaxy, electrochemical characterizations, ambient-pressure X-ray photoelectron spectroscopy, and density functional theory (DFT). We find that inplane compressive strain weakens the surface oxygen binding strength on SrIrO3; however, it has a negligible effect on the surface oxygen electroadsorption and the OER. We explain this observation, which goes against a commonly held intuition that a change in the surface oxygen binding strength should influence surface oxygen electroadsorption and OER by recognizing that the trend in surface oxygen adsorption measured in the gas phase does not account for the presence of water in the surface oxygen electroadsorption. Inclusions of surface water molecules allow DFT to qualitatively reproduce the electroadsorption trend, highlighting the importance of surface water in the surface–oxygen interaction. Our finding suggests that a commonly held assumption between surface oxygen binding strength (in vacuum, no water) and electroadsorption (requiring water) is not always a simple one-to-one description and calls for a more in-depth investigation on the structure of water at electrochemical interfaces.

We report spin-torque ferromagnetic resonance studies of the efficiency of the damping-like (ξ DL ) spin−orbit torque exerted on an adjacent ferromagnet film by current flowing in epitaxial ( 001) and ( 110) IrO 2 thin films. IrO 2 possesses Dirac nodal lines (DNLs) in the band structure that are gapped by spin− orbit coupling, which could enable a very high spin Hall conductivity, σ SH . We find that the (001) films do exhibit exceptionally high ξ DL ranging from 0.45 at 293 K to 0.65 at 30 K, which sets the lower bounds of σ SH to be 1.9 × 10 5 and 3.75 × 10 5 Ω −1 m −1 , respectively, 10 times higher and of opposite sign than the theoretical prediction. Furthermore, ξ DL and σ SH are substantially reduced in anisotropically strained (110) films. We suggest that this high sensitivity to anisotropic strain is because of changes in contributions to σ SH near the DNLs.

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