Transition metal oxides or (oxy)hydroxides have been intensively investigated as promising electrocatalysts for energy and environmental applications. Oxygen in the lattice was reported recently to actively participate in surface reactions. Herein, we report a sacrificial template-directed approach to synthesize Mo-doped NiFe (oxy)hydroxide with modulated oxygen activity as an enhanced electrocatalyst towards oxygen evolution reaction (OER). The obtained MoNiFe (oxy)hydroxide displays a high mass activity of 1910 A/gmetal at the overpotential of 300 mV. The combination of density functional theory calculations and advanced spectroscopy techniques suggests that the Mo dopant upshifts the O 2p band and weakens the metal-oxygen bond of NiFe (oxy)hydroxide, facilitating oxygen vacancy formation and shifting the reaction pathway for OER. Our results provide critical insights into the role of lattice oxygen in determining the activity of (oxy)hydroxides and demonstrate tuning oxygen activity as a promising approach for constructing highly active electrocatalysts.

Conversion reaction enables Li/garnet interface to construct a kinetically stable interfacial layer for the homogeneous ions transport in all-solid-batteries.

The oxygen redox reaction in lithium-rich layered oxide battery cathode materials generates extra capacity at high cell voltages (i.e., >4.5 V). However, the irreversible oxygen release causes transition metal (TM) dissolution, migration and cell voltage decay. To circumvent these issues, we introduce a strategy for tuning the Coulombic interactions in a model Li-rich positive electrode active material, i.e., Li1.2Mn0.6Ni0.2O2. In particular, we tune the Coulombic repulsive interactions to obtain an adaptable crystal structure that enables the reversible distortion of TMO6 octahedron and mitigates TM dissolution and migration. Moreover, this strategy hinders the irreversible release of oxygen and other parasitic reactions (e.g., electrolyte decomposition) commonly occurring at high voltages. When tested in non-aqueous coin cell configuration, the modified Li-rich cathode material, combined with a Li metal anode, enables a stable cell discharge capacity of about 240 mAh g−1 for 120 cycles at 50 mA g−1 and a slower voltage decay compared to the unmodified Li1.2Mn0.6Ni0.2O2.

The redox center of transition metal oxides and hydroxides is generally considered to be the metal site. Interestingly, proton and oxygen in the lattice recently are found to be actively involved in the catalytic reactions, and critically determine the reactivity. Herein, taking glycerol electrooxidation reaction as the model reaction, we reveal systematically the impact of proton and oxygen anion (de)intercalation processes on the elementary steps. Combining density functional theory calculations and advanced spectroscopy techniques, we find that doping Co into Ni-hydroxide promotes the deintercalation of proton and oxygen anion from the catalyst surface. The oxygen vacancies formed in NiCo hydroxide during glycerol electrooxidation reaction increase d-band filling on Co sites, facilitating the charge transfer from catalyst surface to cleaved molecules during the 2nd C-C bond cleavage. Consequently, NiCo hydroxide exhibits enhanced glycerol electrooxidation activity, with a current density of 100 mA/cm2 at 1.35 V and a formate selectivity of 94.3%.

Understanding the catalysis mechanism of the sluggish oxygen evolution reaction (OER) involved in water splitting is of vital importance for the development of clean hydrogen energy. Earthabundant transition-metal (oxy)hydroxide with low cost and high performance is one of the most promising OER catalysts. These catalysts often dynamically and heterogeneously transform from inactive precatalysts into active phases under operation conditions, and thus, the operando/in situ method is needed for the direct observation. Herein, using in situ Raman spectroscopy and density functional theory simulation, we correlate the OER activity with the dynamic crystal-and electronic-structure reconstruction of nano-sheet cobalt hydroxide. A complicated dual-transformation path is observed as the applied voltage is gradually increased; the pristine single-phase α-Co(OH) 2 catalyst transforms into the hydrous Co(OH) 2 phase through hydroxide intercalation, then to mixed β/γ-CoOOH phases through dehydration and dehydrogenation, and finally to OER-active γ-CoOOH x and β-CoOOH y . Moreover, the observed spectral and Tafel behaviors at different scan rates manifest the rate-dependent formation of the dual-active-phase, demonstrating the correlation between the OER ability and thermodynamics of structural reconstruction, which is critical in the fabrication of high-activity catalysts.

Rechargeable aqueous zinc-ion batteries (AZIBs) are close complements to lithium-ion batteries for next-generation grid-scale applications owing to their high specific capacity, low cost, and intrinsic safety. Nevertheless, the viable cathode materials (especially manganese oxides) of AZIBs suffer from poor conductivity and inferior structural stability upon cycling, thereby impeding their practical applications. Herein, a facile synthetic strategy of beadlike manganese oxide coated with carbon nanofibers (MnO x -CNFs) based on electrospinning is reported, which can effectively improve the electron/ion diffusion kinetics and provide robust structural stability. These benefits of MnO x -CNFs are evident in the electrochemical performance metrics, with a long cycling durability (i.e., a capacity retention of 90.6% after 2000 cycles and 71% after 5000 cycles) and an excellent rate capability. Furthermore, the simultaneous insertion of H + /Zn 2+ and the Mn redox process at the surface and in the bulk of MnO x -CNFs are clarified in detail. Our present study not only provides a simple avenue for synthesizing high-performance Mn-based cathode materials but also offers unique knowledge on understanding the corresponding electrochemical reaction mechanism for AZIBs.

Tandem catalysis provides an economical and energy-efficient process for the production of fine chemicals. In this work, we demonstrate that a rationally synthesized carbon-based catalyst with atomically dispersed dual Fe–Al sites (ADD-Fe-Al) achieves superior catalytic activity for the one-pot oxidative carboxylation of olefins (conversion ∼97%, selectivity ∼91%), where the yield of target product over ADD-Fe-Al is at least 62% higher than that of monometallic counterparts. The kinetic results reveal that the excellent catalytic performance arises from the synergistic effect between Fe (oxidation site) and Al sites (cycloaddition site), where the efficient CO2 cycloaddition with epoxides in the presence of Al sites (3.91 wt %) positively shifts the oxidation equilibrium to olefin epoxidation over Fe sites (0.89 wt %). This work not only offers an advanced catalyst for oxidative carboxylation of olefins but also opens up an avenue for the rational design of multifunctional catalysts for tandem catalytic reactions in the future.

High-voltage LiCoO2 (LCO) attracts great interest because of its large specific capacity, but it suffers from oxygen release, structural degradation, and quick capacity drop. These daunting issues root from the inferior thermodynamics and kinetics of the triggered oxygen anion redox (OAR) at high voltages. Herein, a tuned redox mechanism with almost only Co redox is demonstrated by atomically engineered high-spin LCO. The high-spin Co network reduces the Co/O band overlap, eliminates the adverse phase transition of O3 → H1–3, delays the exceeding of the O 2p band over the Fermi level, and suppresses excessive O → Co charge transfer at high voltages. This function intrinsically promotes Co redox and restrains O redox, fundamentally addressing the issues of O2 release and coupled detrimental Co reduction. Moreover, the chemomechanical heterogeneity caused by different kinetics of Co/O redox centers and the inferior rate performance limited by slow O redox kinetics is simultaneously improved owing to the suppression of slow OAR and the excitation of fast Co redox. The modulated LCO delivers ultrahigh rate capacities of 216 mAh g–1 (1C) and 195 mAh g–1(5C), as well as high capacity retentions of 90.4% (@100 cycles) and 86.9% (@500 cycles). This work sheds new light on the design for a wide range of O redox cathodes.