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Spin-sate reconfiguration induced by alternating magnetic field for efficient oxygen evolution reaction.

ABSTRACT: Oxygen evolution reaction (OER) plays a determining role in electrochemical energy conversion devices, but challenges remain due to the lack of effective low-cost electrocatalysts and insufficient understanding about sluggish reaction kinetics. Distinguish from complex nano-structuring, this work focuses on the spin-related charge transfer and orbital interaction between catalysts and intermediates to accelerate catalytic reaction kinetics. Herein, we propose a simple magnetic-stimulation approach to rearrange spin electron occupation in noble-metal-free metal-organic frameworks (MOFs) with a feature of thermal-differentiated superlattice, in which the localized magnetic heating in periodic spatial distribution makes the spin flip occur at particular active sites, demonstrating a spin-dependent reaction pathway. As a result, the spin-rearranged Co_0.8Mn_0.2 MOF displays mass activities of 3514.7 A g_metal^-1 with an overpotential of ~0.27 V, which is 21.1 times that of pristine MOF. Our findings provide a new paradigm for designing spin electrocatalysis and steering reaction kinetics.

SUBMITTER: Zhou G

PROVIDER: S-EPMC8355122 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Spin-polarized oxygen evolution reaction under magnetic field.

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Project description:Currently, energy-efficient electrocatalytic oxygen evolution from water involves the use of noble metal oxides. Here, we show that highly p-conducting zinc cobaltite spinel Zn1.2Co1.8O3.5 offers an enhanced electrocatalytic activity for oxygen evolution. We refer to previous studies on sputtered Zn-Co spinels with optimized conductivity for implementation as (p-type) transparent conducting oxides. Based on that, we manufacture off-stoichiometric conducting p-spinel catalytic anodes on tetragonal Ti, Au-Ti and hexagonal Al-doped ZnO carriers and report the evolution of O2 at Tafel slopes between 40.5 and 48 mV dec-1 and at overpotentials between 0.35 and 0.43 V (at 10 mA cm-2). The anodic stability, i.e., 50 h of continuous O2 electrolysis in 1 M KOH, suggests that increasing the conductivity is advantageous for electrolysis, particularly for reducing the ohmic losses and ensuring activity across the entire surface. We conclude by pointing out the merits of improving p-doping in Zn-Co spinels by optimized growth on a tetragonal Ti-carrier and their application as dimension-stable 3d-metal anodes.

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Project description:Herein, we report high electrocatalytic activity of monoclinic VO2 (M1 phase) for the oxygen evolution reaction (OER) for the first time. The single-phase VO2 (M1) nanoparticles are prepared in the form of uniformly covering the surface of individual carbon fibers constituting a carbon fiber paper (CFP). The VO2 nanoparticles reveal the metal-insulator phase transition at ca. 65 °C (heating) and 62 °C (cooling) with low thermal hysteresis, indicating a high concentration of structural defect which is considered a grain boundary among VO2 nanoparticles with some particle coalescence. Consequently, the VO2/CFP shows a high electrocatalytic OER activity with the lowest η10 (350 mV) and Tafel slope (46 mV/dec) values in a 1 M aqueous solution of KOH as compared to those of the vacuum annealed V2O5 and the hydrothermally grown VO2 (M1), α-V2O5, and γ'-V2O5. The catalytically active site is considered V4+ components and V4+/5+ redox couples in VO2. The oxidation state of V4+ is revealed to be more favorable to the OER catalysis compared to that of V5+ in vanadium oxide through comparative studies. Furthermore, the amount of V5+ component is found to be increased on the surface of VO2 catalyst during the OER, giving rise to the performance degradation. This work suggests V4+ and its redox couple as a novel active component for the OER in metal-oxide electrocatalysts.

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