A General Strategy for Hollow Metal‐Phytate Coordination Complex Micropolyhedra Enabled by Cation Exchange

Hollow CoNiFe ternary metal selenide electrocatalysts derived from Prussian blue analogues for boosting the oxygen evolution reaction

The development of effective electrocatalysts is a top priority for the oxygen evolution reaction (OER), which is the crucial half-reaction of water electrolysis, since electrocatalytic water splitting for hydrogen production offers a practical solution to the upcoming energy crisis. Herein, we report a strategy to fabricate hollow ternary metal selenide (CoNiFe-Se) nanocubes derived from Prussian blue analogues (PBAs) by phytic acid etching and low-temperature gas-phase selenization. Due to the advantages of its multi-component composition and hollow structure, CoNiFe-Se exhibited a low overpotential of 275 mV@10 mA cm-2, a small Tafel slope of 62.3 mV dec-1 and a long-term stability of more than 80 h in 1.0 M KOH. This research offers an innovative idea and a straightforward technique for preparing hollow multimetallic selenide electrocatalysts derived from PBAs.

Lewis Acid Sites in Hollow Cobalt Phytate Micropolyhedra Promote the Electrocatalytic Water Oxidation

The acid-base microenvironment of the metal center is crucial for constructing advanced oxygen evolution reaction (OER) electrocatalysts. However, the correlation between acidic site and OER performance remains unclear for cobalt-based catalysts. Herein, Lewis acid sites in hollow cobalt phytate micropolyhedra (M-CoPA, M = Cu, Sr) were synthesized by a cation-exchange strategy, and their OER performances were studied systematically. Experimentally, Lewis acid Cu2+ sites with stronger Lewis acidity exhibited superior intrinsic activity and long-term stability in alkaline electrolytes. The spectroscopic and electrochemical studies show Lewis acid sites in hollow cobalt phytate micropolyhedra can modulate the electronic distribution of the adjacent cobalt center and further optimize the adsorption strength of oxygenated species. This study figures out the effect of Lewis acid sites on the OER kinetics and provides an effective way to develop high-efficiency electrocatalysts for energy conversion systems.

Synthesis of Sulfur Vacancy-Bearing In2S3/CuInS2 Microflower Heterojunctions via a Template-Assisted Strategy and Cation-Exchange Reaction for Photocatalytic CO2 Reduction

The synthesis of the accurate composition and morphological/structural design of multielement semiconductor materials is considered an effective strategy for obtaining high-performance hybrid photocatalysts. Herein, sulfur vacancy (Vs)-bearing In2S3/CuInS2 microflower heterojunctions (denoted Vs-In2S3/CuInS2) were formed in situ using In2S3 microsphere template-directed synthesis and a metal ion exchange-mediated growth strategy. Photocatalysts with flower-like microspheres can be obtained using hydrothermally synthesized In2S3 microspheres as a template, followed by Ostwald ripening growth during the metal cation exchange of Cu+ and In3+. The optimal heterostructured Vs-In2S3/CuInS2 microflowers exhibited CO and CH4 evolution rates of 80.3 and 11.8 μmol g-1 h-1, respectively, under visible-light irradiation; these values are approximately 4 and 6.8 times higher than those reported for pristine In2S3, respectively. The enhanced photocatalytic performance of the Vs-In2S3/CuInS2 catalysts could be attributed to the synergistic effects of the following factors: (i) the constructed heterojunctions accelerate charge-carrier separation; (ii) the flower-like microspheres exhibit highly uniform morphologies and compositions, which enhance electron transport and light harvesting; and (iii) the vs. may trap excited electrons and, thus, inhibit charge-carrier recombination. This study not only confirms the feasibility of the design of heterostructures on demand, but also presents a simple and efficient strategy to engineer metal sulfide photocatalysts with enhanced photocatalytic performance.

Synergistic effect of composition gradient and morphology on the catalytic activity of amorphous FeCoNi-LDH

The rational design of electrocatalysts with well-designed compositions and structures for the oxygen evolution reaction (OER) is promising and challenging. Herein, we developed a novel strategy - a one-step double-cation etching sedimentation equilibrium strategy - to synthesize amorphous hollow Fe-Co-Ni layered double hydroxide nanocages with an outer surface of vertically interconnected ultrathin nanosheets (Fe-Co-Ni-LDH), which primarily depends on the in situ etching sedimentation equilibrium of the template interface. This unique vertical nanosheet-shell hierarchical nanostructure possesses enhanced charge transfer, increased active sites, and favorable kinetics during electrolysis, resulting in superb electrocatalytic performance for the oxygen evolution reaction (OER). Specifically, the Fe-Co-Ni-LDH nanocages exhibited remarkable OER activity in alkaline electrolytes and achieved a current density of 100 mA cm-2 at a low overpotential of 272 mV with excellent stability. This powerful strategy provides a profound molecular-level insight into the control of the morphology and composition of 2D layered materials.

Biomimetic Construction of Degradable DNAzyme-Loaded Nanocapsules for Self-Sufficient Gene Therapy of Pulmonary Metastatic Breast Cancer

Pulmonary metastasis of breast cancer is the major cause of deaths of breast cancer patients, but the effective treatment of pulmonary metastases is still lacking at present. Herein, a degradable biomimetic DNAzyme biocapsule is developed with the poly(ethylenimine) (PEI)-DNAzyme complex encapsulated in a Mn2+/Zn2+-coordinated inositol hexaphosphate (IP6) capsule modified with the cRGD targeting peptide for high-efficiency gene therapy of both primary and pulmonary metastatic breast tumors. This DNAzyme biocapsule is degradable inside acidic lysosomes, leading to the release of DNAzyme and abundant Mn2+/Zn2+ for catalytic cleavage of EGR-1 mRNA. We find that PEI promotes the lysosomal escape of the released DNAzyme. Both in vitro and in vivo experiments demonstrate the apparent downregulation of EGR-1 and Bcl-2 protein expression after treatment with the DNAzyme biocapsule, thereby inducing apoptotic death of tumor cells. We further verify that the DNAzyme biocapsule exhibits potent therapeutic efficacy against both primary and pulmonary metastatic breast tumors with significant inhibition of peri-pulmonary metastasis. This study provides a promising effective strategy for constructing degradable DNAzyme-based platforms with self-supply of abundant metal ion cofactors for high-efficiency gene therapy of metastatic breast cancer.

A General "In Situ Etch-Adsorption-Phosphatization" Strategy for the Fabrication of Metal Phosphides/Hollow Carbon Composite for High Performance Liquid/Flexible Zn-Air Batteries

Benefiting from the admirable energy density (1086 Wh kg-1 ), overwhelming security, and low environmental impact, rechargeable zinc-air batteries (ZABs) are deemed to be attractive candidates for lithium-ion batteries. The exploration of novel oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts is the key to promoting the development of zinc-air batteries. Transitional metal phosphides (TMPs) especially Fe-based TMPs are deemed to be a rational type of catalyst, however, their catalytic performance still needs to be further improved. Considering Fe (heme) and Cu (copper terminal oxidases) are nature's options for ORR catalysis in many forms of life from bacteria to humans. Herein, a general "in situ etch-adsorption-phosphatization" strategy is designed for the fabrication of hollow FeP/Fe2 P/Cu3 P-N, P codoped carbon (FeP/Cu3 P-NPC) catalyst as the cathode of liquid and flexible ZABs. The liquid ZABs manifest a high peak power density of 158.5 mW cm-2 and outstanding long-term cycling performance (≈1100 cycles at 2 mA cm-2 ). Similarly, the flexible ZABs deliver superior cycling stability of 81 h at 2 mA cm-2 without bending and 26 h with different bending angles.

Surface Engineering over Metal-Organic Framework Nanoarray to Realize Boosted and Sustained Urea Oxidation

Facilitating C─N bond cleavage and promoting *COO desorption are essential yet challenging in urea oxidation reactions (UORs). Herein a novel interfacial coordination assembly protocol is established to modify the Co-phytate coordination complex on the Ni-based metal-organic framework (MOF) nanosheet array (CC/Ni-BDC@Co-PA) toward boosted and sustained UOR electrocatalysis. Comprehensive experimental and theoretical investigations unveil that surface Co-PA modification over Ni-BDC can manipulate the electronic state of Ni sites, and in situ evolved charge-redistributed surface can promote urea adsorption and the subsequent C─N bond cleavage. Impressively, Co-PA functionalization can impart a negatively charged catalyst surface with improved aerophobicity, not only weakening *COO adsorption and promoting CO2 departure, but also repelling CO3 2- approaching to deactivate Ni species, eventually alleviating CO2 poisoning and enhancing operational durability. Beyond that, improved hydrophilic and aerophobic characteristics would also contribute to better mass transfer kinetics. Consequently, CC/Ni-BDC@Co-PA exhibits prominent UOR performance with an ultralow potential of 1.300 V versus RHE to attain 10 mA cm-2 , a small Tafel slope of 45 mV dec-1 , and strong durability, comparable to the best Ni-based electrocatalysts documented thus far. This work affords a novel paradigm to construct MOF-based materials for promoted and sustained UOR catalysis through elegant surface engineering based on a metal-PA complex.

Skeleton-coated CoCu-Based bimetal hollow nanoprisms as High-Performance electrocatalysts for oxygen evolution reaction

CoSx materials with high catalytic activity are considered as promising HER electrocatalysts, but their inherent low electrical conductivity and easy loss of active sites have greatly limited their applications in OER electrocatalysis. Herein, we present a convenient method to synthesize Co-Cu hollow nanoprisms after wrapping and calcining with trithiocyanuric acid (C3H3N3S3) (denoted N-Co-Cu-S-x HNs). The results showed that Cu doping modified the charge density of Co center, leading to the enhancement of the intrinsic activity of the Co3S4 active center, meanwhile wrapping trithiocyanuric acid on the surfaces and calcinating to form N-containing C skeleton as a flexible substrate to encapsulate the catalysts, which effectively protected the active sites inside the catalysts. Notably, the OER catalyst that was optimized by adjusting the metal ratio and controlling the trithiocyanuric acid incorporation exhibited a low overpotential of 306 mV under a current density of 10 mA cm-2 and showed a superior durability of more than 27 h. This work may provide some insights into the preparation of oxygen evolution reaction catalysts with excellent performance through doping transition metals and protecting the internal active sites strategies.

Biodegradable Amorphous Copper Iron Tellurite Promoting the Utilization of Fenton-Like Ions for Efficient Synergistic Cancer Theranostics

The major hurdles of chemodynamic therapy (CDT) are nondegradability and low-efficiency utilization of chemodynamic agents, and intracellular glutathione (GSH)-induced rapid scavenging of hydroxyl radicals (•OH). Here, a biodegradable a-CFT@IP6@BSA agent is reported for efficient cancer therapy by encapsulating amorphous copper iron tellurite nanoparticles (a-CFT NPs) into inositol hexaphosphate (IP6) and bovine serum albumin (BSA). The biggest merits of this agent are the GSH responsive degradation and amorphous structure, allowing the tumor-specific release of plenty of Cu⁺ ions and their high-efficiency utilization for •OH production via the Fenton-like reaction. Besides, the released Cu⁺ ions can deplete the intracellular GSH and thereby protect •OH from scavenging, greatly improving the CDT efficiency. Further, it is found that the a-CFT@IP6@BSA NP treatment down-regulates the levels of glutathione peroxidase 4 and BCL-2, indicating GSH depletion-associated ferroptosis and IP6-induced apoptotic death of cancer cells. Utilizing the T₁/T₂ dual-modal magnetic resonance imaging capability, the a-CFT@IP6@BSA NPs are demonstrated with excellent in vivo anticancer efficiency and have great potential for imaging-guided cancer treatment.

Successive Anion/Cation Exchange Enables the Fabrication of Hollow CuCo2S4 Nanorods for Advanced Oxygen Evolution Reaction Electrocatalysis

Hollow CuCo₂S₄ nanorods (H-CCS-Ns) have been successfully developed via a facile successive anion/cation-exchange method. The outstanding electrocatalytic performance of H-CCS-Ns is mainly attributed to its distinctive hollow structure, which accelerates the electron transfer rate and provides abundant active sites. Moreover, a mechanism study indicates that H-CCS-Ns has highly active octahedral Co³⁺, and the existence of Co³⁺ cations optimizes the adsorption of oxygen-involved intermediates, making H-CCS-Ns a promising OER electrocatalyst. Optimized H-CCS-Ns only need an ultralow overpotential of 220 mV to drive a current density of 10 mA·cm^-2 and exhibit distinguished cycling stability with a negligible fluctuation for 30 h. More impressively, when H-CCS-Ns are assembled with Pt/C for overall water splitting, a voltage as low as 1.545 V is required at a current density of 10 mA·cm^-2, and the catalyst shows outstanding stability for as long as 38 h. This study offers a feasible strategy to design hollow spinel catalysts for efficient OER catalysis.

Versatile Synthesis of Hollow Metal Sulfides via Reverse Cation Exchange Reactions for Photocatalytic CO2 Reduction

Herein, we explore a general Cu_2-x S nanocube template-assisted and reverse cation exchange-mediated growth strategy for fabricating hollow multinary metal sulfide. Unlike the traditional cation exchange method controlled by the metal sulfide constant, the introduction of tri-n-butylphosphine (TBP) can reverse cation exchange to give a series of hollow metal sulfides. A variety of hollow multinary metal sulfide cubic nanostructures has been demonstrated while preserving anisotropic shapes to the as-synthesized templates, including binary compounds (CdS, ZnS, Ag₂ S, PbS, SnS), ternary compound (CuInS₂ , Zn_x Cd_1-x S), and quaternary compound (single-atom platinum anchored Zn_x Cd_1-x S; Zn_x Cd_1-x S-Pt₁ ). Experimental and density functional theory (DFT) calculations show that the hollow metal sulfide semiconductors obtained could significantly improve the separation and migration of photogenerated electron-hole pairs. Owing to the efficient charge transfer, the Zn_x Cd_1-x S-Pt₁ exhibited outstanding photocatalytic performance of CO₂ to CO, with the highest CO generation rate of 75.31 μmol h^-1 .

Exploiting Supramolecular Dynamics in Metal-Phenolic Networks to Generate Metal-Oxide and Metal-Carbon Networks

Supramolecular complexation is a powerful strategy for engineering materials in bulk and at interfaces. Metal-phenolic networks (MPNs), which are assembled through supramolecular complexes, have emerged as suitable candidates for surface and particle engineering owing to their diverse properties. Herein, we examine the supramolecular dynamics of MPNs during thermal transformation processes. Changes in the local supramolecular network including enlarged pores, ordered aromatic packing, and metal relocation arise from thermal treatment in air or an inert atmosphere, enabling the engineering of metal-oxide networks (MONs) and metal-carbon networks, respectively. Furthermore, by integrating photo-responsive motifs (i.e., TiO₂ ) and silanization, the MONs are endowed with reversible superhydrophobic (>150°) and superhydrophilic (≈0°) properties. By highlighting the thermodynamics of MPNs and their transformation into diverse materials, this work offers a versatile pathway for advanced materials engineering.