Bioinspired Hierarchical Tin Oxide Scaffolds for Enhanced Gas Sensing Properties

Nature is greatly capable of providing inspiration for the novel design of functional materials. Herein, the efficient bioreactors’ construction of pollen grains inspires us to mimic them for superior gas sensing application. By developing a facile two-step soakage process and subsequent calcinations, the bioreactors are mimicked fully: (I) biosensitive pollen coats on pollen grains are replaced by gas sensitive tin oxide (SnO₂) coats, and (II) the fine hierarchical scaffolds are maintained by the self-support of newly formed SnO₂ coats. For gas sensing application, as-fabricated SnO₂ microreactors exhibit high and fast responses to nitrogen dioxide (219.5 to NO₂ of 50 ppm) and other gases. The good sensing properties should be indeed ascribed to the specific construction of microreactors, which shows elaborate hierarchical porous structures and large accessible space/surface area favorable for both gas molecule transports and sensing reactions. This present strategy provides us with new insight on the exploring of effective and low-cost gas sensors, and it could further extend to other pollen grains of numerous different morphologies and other types of bioreactors that are abundant in nature

From Water Oxidation to Reduction: Transformation from Ni_<i>x</i>Co_3–<i>x</i>O₄ Nanowires to NiCo/NiCoO_<i>x</i> Heterostructures

A homologous Ni–Co based nanowire catalyst pair, composed of Ni_<i>x</i>Co_3–<i>x</i>O₄ nanowires and NiCo/NiCoO_<i>x</i> nanohybrid, is developed for efficient overall water splitting. Ni_<i>x</i>Co_3–<i>x</i>O₄ nanowires are found as a highly active oxygen evolution reaction (OER) catalyst, and they are converted into a highly active hydrogen evolution reaction (HER) catalyst through hydrogenation treatment as NiCo/NiCoO_<i>x</i> heteronanostructures. An OER current density of 10 mA cm^–2 is obtained with the Ni_<i>x</i>Co_3–<i>x</i>O₄ nanowires under an overpotential of 337 mV in 1.0 M KOH, and an HER current density of 10 mA cm^–2 is obtained with the NiCo/NiCoO_<i>x</i> heteronanostructures at an overpotential of 155 mV. When integrated in an electrolyzer, these catalysts demonstrate a stable performance in water splitting

Oxygen Vacancies Unfold the Catalytic Potential of NiFe-Layered Double Hydroxides by Promoting Their Electronic Transport for Oxygen Evolution Reaction

Oxygen vacancies (Ov) engineering has demonstrated tremendous power to expedite electrocatalytic kinetics for oxygen evolution reaction (OER). The mechanism is elusive, and most of them were attributed to the decoration or creation of active sites. Here, we report the critical role of superficial Ov in enhancing the electronic transport, thereby unfolding the catalytic potential of NiFe-layered double hydroxides for OER. We reveal that the superficial Ov engineering barely regulates the intrinsic catalytic activities but lowers the charge transport resistances by more than one order of magnitude. Loading-dependent electrochemical analysis suggests that the superficial Ov engineering intensively modulates the utilization rate of electronically accessible active sites for OER catalysis. By correlating catalytic activities to charging capacitances of CΦ (related to the absorption of reaction intermediates), we unveil a linear dependence, which indicates switchable catalysis on electronically accessible active sites. Based on the unified experimental and theoretical analysis of the electronic structures, we propose that the superficial Ov imposes electron donation to the conductive band of NiFeOOH, thereby enabling the regulation of electronic transport to switch on/off OER catalysis. The switch effect holds fundamental and technical implications for understanding and designing efficient electrocatalysts