关键词: 无机纤维, 静电纺丝, 电催化水分解, 析氧反应, 析氢反应, 陶瓷纳米纤维, 化学气相沉积, 电催化剂

Abstract:

Objective To fulfil China's strategic goal of "carbon peak and carbon neutrality", the development of green energy has become an inevitable direction. As a renewable clean energy, green hydrogen has attracted extensive attention. Electrocatalytic water splitting is one of the most effective strategies for green hydrogen production. However, the reported hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts suffer from bottlenecks such as slow kinetics and poor stability in acid/alkali electrolytes. This work reports a flexible inorganic micro-nano fiber membrane electrode with high catalytic activity and stability for both HER and OER.

Method A flexible CoTiO₃/ZrO₂-TiO₂ ceramic nanofiber membrane was prepared by electrospinning technique and high-temperature calcination. Then, Ru metal atoms and carbon nanotubes were in-situ anchored on the ceramic nanofibers via impregnation adsorption and chemical vapor deposition (CVD), forming CoRu/ZrO₂-Ti₃O₅/CF. The influence mechanisms of Co and Ru metal loadings on the morphology, micro-nano structure, and HER/OER catalytic performance of the flexible fiber membrane electrode were investigated.

Results It was found through experiments that all fiber membranes exhibited a three-dimensional network structure with randomly interwoven fibers. The CoTiO₃/ZrO₂-TiO₂ consisted of TiO₂, ZrO₂, and CoTiO₃, with uniform diameters and rough textures on the surface. The Brunauer-Emmett-Teller (BET) specific surface area was 7.59 m²/g. Due to poor conductivity and lack of catalytic active sites, the HER and OER performances were relatively poor. Co/ZrO₂-Ti₃O₅/CF and Co_0.2Ru/ZrO₂-Ti₃O₅/CF both consisted of Ti₃O₅, ZrO₂, CoO, and Co. The morphology was similar, with carbon nanotubes densely distributed on the surface. TEM showed that the surface carbon nanotubes of Co_0.2Ru/ZrO₂-Ti₃O₅/CF were uniform and dense, with Co metal nanoparticles wrapped at the top, proving that Co catalyzed their formation as active sites during high-temperature carbonization. HRTEM confirmed the presence of Ti₃O₅ (lattice spacing 0.223 nm corresponding to (121) face), ZrO₂ (lattice spacing 0.209 nm corresponding to (012) face), and Co (lattice spacing 0.204 nm corresponding to (111) face) crystal structures in Co_0.2Ru/ZrO₂-Ti₃O₅/CF. Elemental distribution showed that C, N, Co, and Ru were evenly distributed throughout the entire fiber, while O, Ti, and Zr were mainly within the internal ceramic nanofibers. Moreover, a certain thickness of carbon fiber layer formed on the surface of ZrO₂-Ti₃O₅ ceramic nanofibers in addition to the carbon nanotubes. For CoRu/ZrO₂-Ti₃O₅/CF with Co∶Ti molar ratios of 0∶1, 0.05∶1, 0.1∶1, 0.15∶1, 0.2∶1, and 0.25∶1, Ru/ZrO₂-Ti₃O₅/CF had uniform diameters, smooth surfaces, and no carbon nanotubes. As Co was introduced with increasing loading, the number and length of carbon nanotubes were gradually increased. Raman analysis showed that an increase in Co content led to an increase in I_D:I_Gvalues and an increase in carbon defects. In BET testing, the specific surface area of Co_0.2Ru/ZrO₂-Ti₃O₅/CF was 42.89 m²/g, significantly higher than that of CoTiO₃/ZrO₂-TiO₂. At a current density of 10 mA/cm², Co_0.2/ZrO₂-Ti₃O₅/CF had an HER overpotential of 126 mV and an OER potential of 1.557 V, showing a significant improvement in performance compared to CoTiO₃/ZrO₂-TiO₂. The HER and OER overpotentials of the fiber catalyst decreased first and then increased with the increase in Co loading, while the Tafel slope fell first and then rose. The Co_0.2Ru/ZrO₂-Ti₃O₅/CF had the smallest overpotential and Tafel slope. In a two-electrode system with it as a self-supported catalyst and 1.0 M KOH as the electrolyte for electrocatalytic water splitting testing, only a low voltage of 1.64 V was required to achieve a current density of 10 mA/cm².

Conclusion The synergistic effect of Co-Ru bimetallic sites can effectively enhance the HER and OER bifunctional catalytic performance of CoRu/ZrO₂-Ti₃O₅/CF. In 1 mol/L KOH electrolyte, the flexible self-supporting Co_0.2Ru/ZrO₂-Ti₃O₅/CF fiber membrane electrode exhibits a high HER and OER catalytic performance: when the current density is 10 mA/cm², the overpotential is 103 mV for HER, the OER potential is 1.531 V, and the slope of Tafel is 94 mV/dec, which is superior to the noble metal RuO₂ catalyst. This research can provide new ideas for the preparation of self-supporting electrocatalysts for water splitting.

Key words: inorganic nanofiber, electrospinning, electrocatalytic water splitting, oxygen evolution reaction (OER), hydrogen evolution reaction (HER), ceramic nanofiber, chemical vapor deposition, electrocatalyst