[en] Highlights: • A P2/O3 biphasic structure was constructed in a Fe/Mn-based layered cathode through high-proportion Li/Ti co-substitution. • High-proportion Li substitution triggered the reversible anionic redox activity, thus an ultrahigh capacity (~ 235 mA h g⁻¹). • The unique intersected complex way at the P2/O3 phase boundary greatly enhanced the cycling stability. As the representative layered oxide cathode for sodium ion batteries (SIBs) featuring the low cost, P2-type Na-Fe-Mn oxide (NFMO) delivers a high capacity but a limited cycling stability, while O3-type NFMO shows extended cycling lifespan but a lower capacity. Considering the complementarity of two phases in electrochemistry, we successfully designed and fabricated a Fe/Mn-based layered oxide Na_0.67Li_0.11Fe_0.36Mn_0.36Ti_0.17O₂ with a unique P2/O3 biphasic architecture through high-proportion Li/Ti co-substitution. High-proportion Li substitution in transition metal layers triggers the reversible O redox below 4.2 V due to the formation of the special O bonding environment, delivering a highest capacity of 235 mA h g¹ ever reported among all Fe- and Mn-based layered oxide cathodes. Moreover, the unique intersected complex way at the phase boundary significantly suppressed the P2→OP4 phase transition and decreased the lattice mismatch between two phases at high potentials, greatly enhancing the cycling stability. This novel phase complex strategy benefits the design of promising cathode materials with high capacity and long lifespan for SIBs and beyond.

[en] Highlights: • We show a discrete Fe₂TiO₅-incorporation in hematite to improve the performance. • It can be well coupled with surface P-modification with a synergetic effect. • It shows a high photocurrent of 2.90 mA/cm² at 1.23 VRHE with Co-Pi catalysts. • It provides a good insight to understand other Ti-based treatments of hematite. Hematite is a promising photocatalyst for solar water splitting while its performance has been severely limited by various factors. Recently surface Fe₂TiO₅ layer was widely reported to enhance the performance of hematite with a favorable band position to facilitate hole transport. Here we further show that the Fe₂TiO₅-incorporation in bulk hematite can also improve the performance with faster charge separation. Moreover, it can be well coupled with surface P-modification to simultaneously improve charge separation and hole transfer with a synergetic effect. The Ti and P co-modified hematite shows a significantly enhanced photocurrent of 2.37 mA/cm² at 1.23 V vs. RHE when compared to the pristine value of 0.85 mA/cm². After coupling with Co-Pi catalysts, the hematite sample can even achieve a stable, high photocurrent of 2.90 mA/cm² at 1.23 V vs. RHE. The design of Ti and P co-modified hematite hollow nanostructures can be used as a promising candidate for solar water splitting applications. The discrete Fe₂TiO₅-incorporation also provides a good insight on the mechanism to understand other Ti-based treatments of hematite.

[en] Li-rich layered oxides based on the anionic redox chemistry provide the highest practical capacity among all transition metal (TM) oxide cathodes but still struggle with poor cycling stability. Here, a certain amount of oxygen vacancies (OVs) are introduced into the ≈10 nm-thick surface region of Li${}_{1.2}$Ni${}_{0.13}$Co${}_{0.13}$Mn${}_{0.54}$O${}_2$ through a long-time medium-temperature post-annealing. These surficial enriched OVs significantly suppress the generation of O-O dimers (O${}_2$${}^{n-<!--\; ???\; -->}$, 0 < n < 4) and the associated side reactions, thus facilitating the construction of a uniform and compact cathode/electrolyte interphase (CEI) layer on the surface. The CEI layer then decreases the further side reactions and TM dissolution and protects the bulk structure upon cycling, eventually leading to enhanced cycling stability, demonstrated in both half cells and full cells. An in-depth understanding of OVs is expected to benefit the design of stable cathode materials based on anionic redox chemistry. (© 2023 Wiley‐VCH GmbH)

[en] Highlights: • Spontaneous electron enrichment at the apexes of BiVO₄ nanopyramid-arrays. • Anisotropic charge separation due to the intrinsic electron induced electric field. • Excess photoexcited holes at the (112) facet apex for highly selective CoPi growth. • Metal-to-ligand charge transfer process within CoPi affect by V 3d electrons. • Correlation between unique structural property and electronic structure demonstrated. The observation of a spontaneous electron enrichment at the apexes of bismuth vanadate (BiVO₄) nanopyramidal arrays is achieved by performing synchrotron-based angular dependent X-ray absorption spectroscopy. In accordance with density function theory calculations, the formation of (112) facets enriched apexes is proposed. Such intrinsically electron-enriched (112) facets at the apexes produce a potential facilitating the diffusion of photoexcited holes, which not only mitigates the recombination with the photoexcited electrons, but also provide an active reaction site for the photoassisted selective growth of cobalt phosphate (CoPi), a well known and highly active co-catalyst for water oxidation at the apex of BiVO₄ nanopyramids. Benefiting from the element-resolved properties of synchrotron-based X-ray spectroscopy, 3d electrons on the vanadium site are directly resolved by resonant inelastic X-ray scattering measurements. Due to this unique morphology, the charge at the apex is expected to induce a strong interaction with CoPi, as a result of the metal-to-ligand charge transfer spectroscopy feature observed from the cobalt site. Substantial evidences are collected by means of comprehensive soft X-ray spectroscopy techniques with high spectral resolution revealing the atomic-scale origin and the nature of the synergy as well as the strong correlation between its unique structural properties and the electronic structure of this novel highly-ordered hybrid photocatalyst and its significantly improved photoelectrochemical performance.