One promising approach to hydrogen energy utilization from full water splitting relies on the successful development of earth-abundant, efficient, and stable electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Here, homologous Co–Ni-based nanotube/nanosheet structures with tunable Co/Ni ratios, including hydroxides and nitrides, are grown on conductive substrates by a cation-exchanging method to grow hydroxides, followed by anion exchanging to obtain corresponding nitrides. These hydroxide OER catalysts and nitride HER catalysts exhibit low overpotentials, small Tafel slopes, and high current densities, which are attributed to their large electrochemically reactive surface, 1D morphologies for charge conduction, and octahedral coordination states of metal ions for efficient catalytic activities. The homologous Co–Ni-based nanotube hydroxides and nitrides suggest promising electrocatalysts for full water splitting with high efficiency, good stability, convenient fabrication, and low cost.

Core–shell heterostructured nanomaterials with mesopores have enormous potential applications in diverse fields. Herein, we report a facile extended Stöber method to synthesize core–shell heterostructured semiconducting nanomaterials with mesoporosity. Silver (Ag) metal-assisted chemically wet etched p-type silicon nanowires (Si NWs) were used as the core, and layer-controllable mesoporous n-type anatase TiO₂ was grown as the shell to successfully fabricate the core–shell p-Si@mesoporous n-TiO₂ hybrid materials. Detailed characterization reveals that the TiO₂ shell was composed of aggregated crystalline TiO₂ nanoparticles with diameters of ≈15 nm, where the TiO₂ coating thickness was tuned ≈50 nm. The interstitial pores of these nanoparticles were observed with average pore sizes of 4–8 nm. The core–shell structured p-Si@mesoporous n-TiO₂ hybrid materials were demonstrated as photocathodes for the solar-driven photoelectrochemical (PEC) production of H₂ at the semiconductor/electrolyte interface.

A homologous Ni–Co based nanowire system, consisting of both nickel cobalt oxide and nickel cobalt sulfide nanowires, is developed for efficient, complementary water splitting. The spinel-type nickel cobalt oxide (NiCo₂O₄) nanowires are hydrothermally synthesized and can serve as an excellent oxygen evolution reaction catalyst. Subsequent sulfurization of the NiCo₂O₄ nanowires leads to the formation of pyrite-type nickel cobalt sulfide (Ni_0.33Co_0.67S₂) nanowires. Due to the 1D nanowire morphology and enhanced charge transport capability, the Ni_0.33Co_0.67S₂ nanowires function as an efficient, stable, and robust nonnoble metal electrocatalyst for hydrogen evolution reaction (HER), substantially exceeding CoS₂ or NiS₂ nanostructures synthesized under similar methods. The Ni_0.33Co_0.67S₂ nanowires exhibit low onset potential of −65, −39, and −50 mV versus reversible hydrogen electrode, Tafel slopes of 44, 68, and 118 mV dec⁻¹ at acidic, neutral, and basic conditions, respectively, and excellent stability, comparable to the best reported non-noble metal-based HER catalysts. Furthermore, the homologous Ni_0.33Co_0.67S₂ nanowires and NiCo₂O₄ nanowires are assembled into an all-nanowire based water splitting electrolyzer with a current density of 5 mA cm⁻² at a voltage as 1.65 V, thus suggesting a unique homologous, earth abundant material system for water splitting.

Plant leaves represent a unique 2D/1D heterostructure for enhanced surface reaction and efficient mass transport. Inspired by plant leaves, a 2D/1D CoO_x heterostructure is developed that is composed of ultrathin CoO_x nanosheets further assembled into a nanotube structure. This bio-inspired architecture allows a highly active Co²⁺ electronic structure for an efficient oxygen evolution reaction (OER) at the atomic scale, ultrahigh surface area (371 m² g⁻¹) for interfacial electrochemical reaction at the nanoscale, and enhanced transport of charge and electrolyte over CoO_x nanotube building blocks at the microscale. Consequently, this CoO_x nanosheet/nanotube heterostructure demonstrates a record-high OER performance based on cobalt compounds reported so far, with an onset potential of ≈1.46 V versus reversible hydrogen electrode (RHE), a current density of 51.2 mA cm⁻² at 1.65 V versus RHE, and a Tafel slope of 75 mV dec⁻¹. Using the CoO_x nanosheet/nanotube catalyst and a Pt-mesh, a full water splitting cell with a 1.5-V battery is also demonstrated.

Photoelectrochemical sensing represents a unique means for chemical and biological detection, with foci of optimizing semiconductor composition and electronic structures, surface functionalization layers, and chemical detection methods. Here, we have briefly discussed our recent developments of TiO₂ nanowire-based photoelectrochemical sensing, with particular emphasis on three main detection mechanisms and corresponding examples. We have also demonstrated the use of the photoelectrochemical sensing of real-time molecular reaction kinetic measurements, as well as direct interfacing of living cells and probing of cellular functions.

Single-layered two-dimensional (2D) ultrathin mesoporous polymer/carbon films are grown by self-assembly of monomicelles at the interfaces of various substrates, which is a general and common modification strategy. These unconventional 2D mesoporous films possess only a single layer of mesopores, while the size of the thin films can grow up to inch size in the plane. Free-standing transparent mesoporous carbon ultrathin films, together with the ordered mesoporous structure on the substrates of different compositions (e.g. metal oxides, carbon) and morphologies (e.g. nanocubes, nanodiscs, flexible and patterned substrates) have been obtained. This strategy not only affords controllable hierarchical porous nanostructures, but also appends the easily modified and multifunctional properties of carbon to the primary substrate. By using this method, we have fabricated Fe₂O₃–mesoporous carbon photoelectrochemical biosensors, which show excellent sensitivity and selectivity for glutathione.

Single-layered two-dimensional (2D) ultrathin mesoporous polymer/carbon films are grown by self-assembly of monomicelles at the interfaces of various substrates, which is a general and common modification strategy. These unconventional 2D mesoporous films possess only a single layer of mesopores, while the size of the thin films can grow up to inch size in the plane. Free-standing transparent mesoporous carbon ultrathin films, together with the ordered mesoporous structure on the substrates of different compositions (e.g. metal oxides, carbon) and morphologies (e.g. nanocubes, nanodiscs, flexible and patterned substrates) have been obtained. This strategy not only affords controllable hierarchical porous nanostructures, but also appends the easily modified and multifunctional properties of carbon to the primary substrate. By using this method, we have fabricated Fe₂O₃–mesoporous carbon photoelectrochemical biosensors, which show excellent sensitivity and selectivity for glutathione.

While electrochemical water splitting is one of the most promising methods to store light/electrical energy in chemical bonds, a key challenge remains in the realization of an efficient oxygen evolution reaction catalyst with large surface area, good electrical conductivity, high catalytic properties, and low fabrication cost. Here, a facile solution reduction method is demonstrated for mesoporous Co₃O₄ nanowires treated with NaBH₄. The high-surface-area mesopore feature leads to efficient surface reduction in solution at room temperature, which allows for retention of the nanowire morphology and 1D charge transport behavior, while at the same time substantially increasing the oxygen vacancies on the nanowire surface. Compared to pristine Co₃O₄ nanowires, the reduced Co₃O₄ nanowires exhibit a much larger current of 13.1 mA cm^-2 at 1.65 V vs reversible hydrogen electrode (RHE) and a much lower onset potential of 1.52 V vs RHE. Electrochemical supercapacitors based on the reduced Co₃O₄ nanowires also show a much improved capacitance of 978 F g^-1 and reduced charge transfer resistance. Density-functional theory calculations reveal that the existence of oxygen vacancies leads to the formation of new gap states in which the electrons previously associated with the Co-O bonds tend to be delocalized, resulting in the much higher electrical conductivity and electrocatalytic activity.

A facile approach for the synthesis of ultralight iron oxide hierarchical structures with tailorable macro- and mesoporosity is reported. This method entails the growth of porous Prussian blue (PB) single crystals on the surface of a polyurethane sponge, followed by in situ thermal conversion of PB crystals into three-dimensional mesoporous iron oxide (3DMI) architectures. Compared to previously reported ultralight materials, the 3DMI architectures possess hierarchical macro- and mesoporous frameworks with multiple advantageous features, including high surface area (ca. 117 m² g⁻¹) and ultralow density (6–11 mg cm⁻³). Furthermore, they can be synthesized on a kilogram scale. More importantly, these 3DMI structures exhibit superparamagnetism and tunable hydrophilicity/hydrophobicity, thus allowing for efficient multiphase interfacial adsorption and fast multiphase catalysis.

A facile approach for the synthesis of ultralight iron oxide hierarchical structures with tailorable macro- and mesoporosity is reported. This method entails the growth of porous Prussian blue (PB) single crystals on the surface of a polyurethane sponge, followed by in situ thermal conversion of PB crystals into three-dimensional mesoporous iron oxide (3DMI) architectures. Compared to previously reported ultralight materials, the 3DMI architectures possess hierarchical macro- and mesoporous frameworks with multiple advantageous features, including high surface area (ca. 117 m² g⁻¹) and ultralow density (6–11 mg cm⁻³). Furthermore, they can be synthesized on a kilogram scale. More importantly, these 3DMI structures exhibit superparamagnetism and tunable hydrophilicity/hydrophobicity, thus allowing for efficient multiphase interfacial adsorption and fast multiphase catalysis.

Semiconducting silicon nanowires (SiNWs) represent one of the most interesting research directions in nanoscience and nanotechnology, with capabilities of realizing structural and functional complexity through rational design and synthesis. The exquisite control of chemical composition, structure, morphology, doping, and assembly of SiNWs, in both individual and array format, as well as incorporation with other materials, offers a nanoscale building block with unique electronic, optoelectronic, and catalytic properties, thus allowing for a variety of exciting opportunities in the fields of life sciences and renewable energy. This review provides a brief summary of SiNW research in the past decade, from the SiNW synthesis by both the top-down approaches and the bottom-up approaches, to several important biological and energy applications including biomolecule sensing, interfacing with cells and tissues, lithium-ion batteries, solar cells, and photoelectrochemical conversion.