Muthukumar Pandi, Nantheeswaran Periyappan, Mariappan Mariappan, Pannipara Mehboobali, Al-Sehemi Abdullah G, Anthony Savarimuthu Philip
Department of Chemistry, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai-600077, Tamil Nadu, India.
Department of Chemistry, SRM IST, Kattankulathur, Chennai-603203, Tamil Nadu, India.
Dalton Trans. 2023 Apr 4;52(14):4606-4615. doi: 10.1039/d3dt00547j.
Highly efficient and stable Earth abundant transition metal electrocatalysts are in great demand for the oxygen evolution reaction (OER), a bottleneck process involved in the water splitting reaction and metal-air batteries. Herein, we have demonstrated a single step direct fabrication of cobalt hydroxide (Co(OH)) nanowires doped with vanadium(V) in a less stable +4 oxidation state and fluoride (F) ions (V-Co(OH)) on a carbon cloth electrode that showed highly enhanced OER activity under alkaline conditions. V-Co(OH) nanowires synthesized under the optimized conditions produced excellent OER activity with an ultralow overpotential of 136 mV at 10 mA cm (scan rate 1 mV s), a small Tafel slope (51.6 mV dec) and good stability over 72 h. To the best of our knowledge, this is the lowest overpotential reported for cobalt-based electrocatalysts to achieve a geometric current density of 10 mA cm. The controlled synthesis and HR-TEM studies revealed the formation of hybrid nanostructures (nanowires along with spherical assembly of nanoparticles) and codoping of V and F ions played an important role in enhancing the OER activity. The detailed chemical composition and oxidation state analysis by X-ray photoelectron spectroscopy (XPS) confirmed the doping of V and ionic F in V-Co(OH) with mixed valence states of Co/Co and a higher Co ratio. The outstanding OER activity of V-Co(OH) is attributed to the formation of a spherical assembly of nanoparticles with nanowires, which provided a high number of catalytically active sites with enhanced charge transport, and doping of higher valence V and strongly electronegative F in V-Co(OH) with a higher ratio of Co/Co promoted OOH* intermediate generation and significantly boosted the OER activity. Overall, the present work highlights the possibility of achieving highly active Earth abundant OER electrocatalysts by controlling the mixed oxidation state of Co with a judicious choice of dopants along with maintaining optimal nanostructure morphologies.
高效且稳定的、地球上储量丰富的过渡金属电催化剂对于析氧反应（OER）的需求十分迫切，析氧反应是水分解反应和金属空气电池中的一个瓶颈过程。在此，我们展示了在碳布电极上一步直接制备掺杂处于较不稳定的 +4 氧化态的钒（V）和氟（F）离子的氢氧化钴（Co(OH)）纳米线（V-Co(OH)），该电极在碱性条件下表现出高度增强的 OER 活性。在优化条件下合成的 V-Co(OH) 纳米线具有出色的 OER 活性，在 10 mA cm（扫描速率 1 mV s）时过电位超低，为 136 mV，塔菲尔斜率小（51.6 mV dec），且在 72 小时内稳定性良好。据我们所知，这是钴基电催化剂在达到 10 mA cm 的几何电流密度时所报道的最低过电位。可控合成和高分辨透射电子显微镜研究表明形成了混合纳米结构（纳米线以及纳米颗粒的球形组装体），并且 V 和 F 离子的共掺杂在增强 OER 活性方面起到了重要作用。通过 X 射线光电子能谱（XPS）进行的详细化学成分和氧化态分析证实了 V 和离子 F 在 V-Co(OH) 中的掺杂，其中 Co 具有 Co/Co 的混合价态且 Co 比例更高。V-Co(OH) 出色的 OER 活性归因于纳米线与纳米颗粒的球形组装体的形成，这提供了大量具有增强电荷传输能力的催化活性位点，并且在 V-Co(OH) 中以较高比例的 Co/Co 掺杂更高价的 V 和强电负性的 F 促进了 OOH* 中间体的生成并显著提高了 OER 活性。总体而言，当前工作突出了通过明智地选择掺杂剂控制 Co 的混合氧化态以及维持最佳纳米结构形态来实现高活性的、地球上储量丰富的 OER 电催化剂的可能性。
