This paper presents a three-dimensional annealed tungsten trioxide nanowire/graphene sheet (3D annealed WO₃ NWs/GS) foam as an excellent and low-cost electrocatalyst. It was prepared using vanadium redox flow battery (VRFB) electrodes through an in situ self-assembly of graphene sheets prepared by mild chemical reduction, followed by freeze-drying and annealing. The 3D annealed WO₃ NWs/GS foam exhibits the highest electrocatalytic activities toward V²⁺/V³⁺ and VO²⁺/VO₂⁺ redox couples among all the tested samples. Charge–discharge tests further confirm that a single flow cell of a VRFB using the 3D annealed WO₃ NWs/GS foam demonstrates excellent energy efficiencies of 79.49% and 83.73% at current densities of 80 mA cm⁻² and 40 mA cm⁻², respectively, which are much higher than those of cells assembled with pristine graphite felt (GF) and 3D WO₃ NWs/GS foam without annealing treatment. Moreover, it shows no obvious degradation after 50 charge–discharge cycles. These results are attributed to the formation of new W–O–C bonds, confirming that the WO₃ NWs are anchored strongly to the GS, which is key to facilitating the redox reactions of the vanadium redox couples. Moreover, the 3D annealed WO₃ NWs/GS foam exhibits a 3D hierarchical porous structure, which can provide more surface electroactive sites to improve the electrochemical performance of VRFBs.

中文翻译：

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三维退火WO ₃纳米线/石墨烯泡沫作为所有钒氧化还原液流电池的电催化材料

本文提出了一种三维退火的三氧化钨纳米线/石墨烯片（3D退火的WO ₃ NWs / GS）泡沫材料，它是一种出色的低成本电催化剂。它是使用钒氧化还原液流电池（VRFB）电极通过通过轻度化学还原制得的石墨烯片原位自组装，然后进行冷冻干燥和退火而制备的。在所有测试样品中，经过3D退火的WO ₃ NWs / GS泡沫对V ²⁺ / V ³⁺和VO ²⁺ / VO ₂ ⁺氧化还原对表现出最高的电催化活性。充放电测试进一步证实了使用3D退火WO ₃的VRFB的单个流通池NWs / GS泡沫在电流密度分别为80 mA cm ^-2和40 mA cm ^-2时分别显示出79.49％和83.73％的出色能效，这比用原始石墨毡（GF）和3D组装的电池要高得多WO ₃ NWs / GS泡沫，未经退火处理。此外，在50次充放电循环后，它没有显示出明显的退化。这些结果归因于新的W–O–C键的形成，证实WO ₃ NW牢固地锚固在GS上，这是促进钒氧化还原对的氧化还原反应的关键。此外，3D退火的WO ₃ NWs / GS泡沫具有3D分层多孔结构，可提供更多的表面电活性位点，从而改善VRFB的电化学性能。