氮掺杂石墨烯气凝胶负载的钌纳米晶用于宽pH范围析氢反应

Nitrogen‐doped graphene aerogel‐supported ruthenium nanocrystals for pH‐universal hydrogen evolution reaction

析氢反应(HER)是电解水过程中的关键半反应之一,设计和合成高性能、低成本的HER电催化剂至关重要.铂(Pt)基电催化剂是酸性、碱性和中性电解质中最有效的HER催化剂,但高昂的价格制约了其广泛应用.钌(Ru)基纳米材料具有高HER活性、稳定性以及相对较低的成本(Ru金属的价格仅为Pt金属的1/20‒1/4),是替代铂基HER电催化剂的理想电极材料,因此,发展简单高效的高活性Ru基HER催化剂合成方法具有重要意义.本文以还原氧化石墨烯和钌-聚烯丙胺(RuⅢ-PAA)络合物为前驱体,采用简单的吸附-热解策略,合成了高质量的氮掺杂石墨烯气凝胶负载的钌纳米晶纳米复合材料(Ru-NCs/N-GA).能量色散X射线光谱、扫描电子显微镜、透射电子显微镜等结果表明,RuⅢ-PAA络合物能够均匀吸附于三维多孔石墨烯气凝胶表面,作为氮(N)源和Ru源;Ru-NCs/N-GA纳米复合材料和无氮掺杂的Ru-NCs/GA纳米复合材料均具有三维多孔结构,有利于催化剂与电解质的充分接触,从而加速了电催化反应过程中的传质.在Ru-NCs/N-GA中,超小的钌纳米晶均匀地锚定在氮掺杂的石墨烯气凝胶表面,而无氮掺杂的Ru-NCs/GA纳米复合物中钌纳米晶团聚非常严重,表明氮的掺杂对于控制钌的晶粒尺寸非常重要.随着处理温度的升高,钌纳米晶的粒子尺寸和基底的导电性增加,但缺陷程度有所下降,在900°C热处理所获得10 wt%Ru-NCs/N-GA-900纳米复合材料具有良好的钌纳米晶分散性(钌纳米粒子尺寸仅为2.3 nm).HER电化学测试结果表明,Ru-NCs/N-GA-900纳米复合材料在1 mol/L HClO4和1 mol/L KOH电解液中仅需要52和36 mV的过电位即可达到10 mA cm^(−2)的电流密度,与20 wt%Pt/C电催化剂HER性能相当,且优于其他温度处理的Ru-NCs/N-GA和目前报道的大部分Ru基HER电催化剂.与此同时,Ru-NCs/N-GA-900纳米复合材料也显示出良好的HER稳定性.Ru-NCs/N-GA纳米复合材料中Ru纳米晶的超细尺寸以及高分散性、钌与氮掺杂石墨烯之间协同作用、氮原子对钌原子的锚定功能贡献到Ru-NCs/N-GA-900纳米复合材料优异的HER活性和稳定性.综上,本文以简单的吸附-热解策略制备了低钌负载量的用于宽pH范围的氮掺杂石墨烯气凝胶支撑的钌纳米晶,其性能可媲美商业化Pt/C催化剂,在电解水制氢领域具有良好的工业化应用前景.

The design and synthesis of high‐performance and low‐cost electrocatalysts for the hydrogen evolution reaction(HER),a key half‐reaction in water electrolysis,are essential.Owing to their modest hydrogen adsorption energy,ruthenium(Ru)‐based nanomaterials are considered outstanding candidates to replace the expensive platinum(Pt)‐based HER electrocatalysts.In this study,we developed an adsorption‐pyrolysis method to construct nitrogen(N)‐doped graphene aerogel(N‐GA)‐supported ultrafine Ru nanocrystal(Ru‐NC)nanocomposites(Ru‐NCs/N‐GA).The particle size of the Ru‐NCs and the conductivity of the N‐GA substrate can be controlled by varying the pyrolysis temperature.Optimal experiments reveal revealed that 10 wt%Ru‐NCs/N‐GA nanocomposites require overpotentials of only 52 and 36 mV to achieve a current density of 10 mA cm^(−2) in 1 mol/L HClO4 and 1 mol/L KOH electrolytes for HER,respectively,which is comparable to 20 wt%Pt/C electrocatalyst.Benefiting from the ultrafine size and uniform dispersion of the Ru‐NCs,the synergy between Ru and the highly conductive substrate,and the anchoring effect of the N atom,the Ru‐NCs/N‐GA nanocomposites exhibit excellent activity and durability in the pH‐universal HER,thereby opening a new avenue for the production of commercial HER electrocatalysts.