Perovskite oxide is an attractive low-cost alternative catalyst for oxygen evolution reaction (OER) relative to the precious metal oxide-based electrocatalysts (IrO and RuO). In this work, a series of Sr-doped La-based perovskite oxide catalysts with compositions of LaSr FeO ( x = 0, 0.2, 0.5, 0.8, and 1) are synthesized and characterized. The OER-specific activities in alkaline solution increase in the order of LaFeO (LF), LaSrFeO (LSF-0.2), LaSrFeO (LSF-0.5), SrFeO (SF), and LaSrFeO (LSF-0.8). We establish a direct correlation between the enhancement in the specific activity and the amount of surface oxygen vacancies as well as the surface Fe oxidation states. The improved specific activity for LSF-0.8 is clearly linked to the optimum amount of surface oxygen vacancies and surface Fe oxidation states. We also find that the OER performance stability is a function of the crystal structure and the deviation in the surface La and/or Sr composition(s) from their bulk stoichiometric compositions. The cubic structure and lower deviation, as is the case for LSF-0.8, led to a higher OER performance stability. These surface performance relations provide a promising guideline for constructing efficient water oxidation.

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Although metallic ruthenium (Ru) is a potential electrocatalyst for the hydrogen evolution reaction (HER) to replace platinum (Pt) at a cost of only ≈4% of Pt, the persistent dissolution of Ru under operation conditions remains a challenge. Here, it is reported that agglomerates of large ruthenium phosphide (RuP) particles (L-RP, ≈32 nm) show outstanding HER performance in pH-universal electrolytes, which particularly demonstrates a surprisingly higher intrinsic activity and durability than small nanoparticles of RuP (S-RP, ≈3 nm) or metallic Ru on carbon supports. This is especially true in basic media, achieving electrocatalytic activity comparable to or even outperforming that of Pt/C, as reflected by lower overpotential at 10 mA cm , smaller Tafel slope, larger exchange current density, and higher turnover frequency while maintaining 200 h stable operation. Calculations suggest that ΔG of RuP is much closer to zero than that of metallic Ru, and phosphorous doping is proven to enhance the rate of proton transfer in HER, contributing in part to the improved activity of RuP. The better performance of L-RP than that of S-RP is ascribed largely to the stabilization of the P species due to the lowered surface energy of large particles. Furthermore, the relatively low-cost materials and facile synthesis make L-RP/C a highly attractive next-generation HER electrocatalyst.

The oxygen evolution reaction (OER) is of prime importance in multiple energy storage devices. Perovskite oxides involving lattice‐oxygen oxidation are generally regarded as highly active OER catalysts, but the deprotonation of surface‐bound intermediates limit the further activity improvement. Here, it is shown that this kinetic limitation can be removed by introducing Sr3B2O6 (SB) which activates a proton‐acceptor functionality to boost OER activity. As a proof‐of‐concept example, an experimental validation is conducted on the extraordinary OER performance of a Sr(Co0.8Fe0.2)0.7B0.3O3−δ (SCFB‐0.3) hybrid catalyst, made using Sr0.8Co0.8Fe0.2O3−δ as active component and SB as a proton acceptor. This smart hybrid exhibits an exceptionally ultrahigh OER activity with an extremely low overpotential of 340 mV in 0.1 m KOH and 240 mV in 1 m KOH required for 10 mA cm−2 which is the top‐level catalytic activity among metal oxides reported so far, while maintaining excellent durability. The correlation of pH and activity study reveals that this enhanced activity mainly originates from the improved interfacial proton transfer. Such a strategy further demonstrated to be universal, which can be applied to enhance the OER activity of other high covalent oxides with close O 2p‐band centers relative to Fermi energy.

Molybdenum carbide (MoxC) with variable phase structure possesses flexible hydrogen‐binding energy (HBE), which is a promising hydrogen evolution reaction (HER) catalyst. Herein, a hybrid multiphase MoxC freestanding film coupled with Co3Mo (CM/MoxC@NC) is synthesized through the electrospinning method supplemented by the heteroatom incorporation. CM/MoxC@NC surpasses its pure phase counterparts and exhibits remarkable catalytic activity at 114 mV to deliver a current density of 10 mA cm−2 in acid, which is among the first‐rate level performance reported for MoxC‐based catalysts. The subsequent ex situ and in situ characterizations reveal a phase transition mechanism based on self‐catalysis that CoOx depletes the coordinated C of α‐MoC via the interaction, which realizes the assembly of weak HBE α‐MoC and strong HBE β‐Mo2C, and the enhanced utilization of active materials as well. The multiple structures with optimal HBE are in favor of the stepwise reactions of HER, as the study of the correlation between HBE and phase structure revealed. This study discloses the underlying phase transition mechanism and highlights the HBE–structure relationship that should be considered for catalyst design.

Layered A x CoO 2 materials built by stacking layers of CoO 2 slabs and inserting alkali ions in between them have shown a promising activity of oxygen evolution reaction (OER) due to their active edge sites. However, the large basal plane areas of the CoO 2 slabs show too strong adsorption energy to the reaction intermediates, which is unfavorable for the release of O 2 . Here, a simple cation-exchange strategy based on Fe 3+ and alkali ions is proposed to simultaneously activate both the basal plane and edge sites of A x CoO 2 for the OER. X-ray absorption spectroscopy has revealed that the Fe 3+ ions deposit both on the surface and edge sites of the CoO 2 slabs and enter the interlayer. The cation-exchanged A x CoO 2 electrodes show a boosted activity compared to their pristine and conventional Fe-doped A x CoO 2 counterparts. This phenomenon is mainly ascribed to the abundant edge-sharing Co-Fe motifs at the edge sites and the charge redistribution in the basal plane sites induced by the insertion of Fe 3+ ions. This work provides a novel method to fully exploit layer-structured materials for efficient energy conversion.

The cycling performance of Li−O 2 batteries (LOBs), which is an important parameter determining the practical use of this advanced energy technology with ultrahigh energy density, is strongly affected by the nature of the oxygen electrocatalyst. As a good oxygen electrode, it should possess good activity for both the oxygen evolution reaction and the oxygen reduction reaction and superior stability under operating conditions. During the past, oxygen electrodes for LOBs were generally fabricated by loading noble metal nanoparticles on the surface of a porous carbon support. However, the nanoparticles could easily lose contact with the carbon support during the reversible liquid−gas− solid reactions that involve lithium ions, oxygen gas, and Li 2 O 2 . Herein, we reported a novel Ru-metal−organic framework (MOF)-derived carbon composite, characterized by stereoscopic Ru nanoparticle distribution within the carbon matrix, as an alternative oxygen catalyst of LOBs, enabling superior operational stability and favorable activity. More specifically, the battery demonstrated stable charge−discharge cycling for up to 800 times (∼107 days) at a current density of 500 mA g −1 with low discharge/charge overpotentials (∼0.2/0.7 V vs Li). A mechanism of regenerative surface was further proposed to explain the excellent cycling stability of the LOBs through the use of the Ru-MOF−C catalyst. These encouraging results imply an accessible solution to address issues related to the oxygen catalyst for the realization of practical LOBs.

A sluggish oxygen evolution reaction (OER) is a central issue for many chemical and energy transformation technologies, necessitating the development of cost-effective electrocatalysts to accelerate the reaction rate. A recent study has demonstrated that the intrinsic activity of catalysts is strongly associated with diverse electronic structure parameters; therefore, designing an effective strategy to optimize electronic structures in multiple aspects is highly attractive for realizing high-performance OER catalysts. Here, we report a facile A/B-site cosubstitution strategy to regulate the electronic structures of oxygen-deficient brownmillerite oxides for optimizing the OER performance. Cosubstitution of strontium and cobalt into Ca2Fe2O5 parent oxide is found to be very effective in enhancing the OER catalytic performance. Combined soft X-ray absorption spectroscopy analysis and density functional theory calculations show that optimized CaSrCoFeO6−δ (CSCF) is endowed with multiple advantageous electronic structure features for OER catalysis including favorable valence, orbital, and spin states of metal ions and an upshifted O 2p-band center as well as high metal–oxygen covalency. Benefiting from these ideal electronic structure parameters, CSCF exhibits ultrahigh OER activity with a low overpotential of only 330 mV at 10 mA cm–2 in 0.1 M KOH, outperforming noble metal RuO2 and various state-of-the-art metal oxides ever reported while maintaining robust stability as evidenced by operando spectroscopy.