金属-有机框架原位转化合成无定形Fe基双金属氢氧化物催化剂催化析氧反应性能

传统化石能源的大量消耗使得能源短缺和环境污染等问题日益严峻.社会的可持续发展需要进行能源结构调整,寻求清洁、可再生的替代能源已迫在眉睫.氢能作为一种可再生能源,其热值高,燃烧产物无污染,是未来最理想的能源形式之一.水裂解制氢是公认的未来清洁制氢的一种有效途径.然而,无论是电催化或光催化水裂解反应,析氧反应都是关键的半反应.因其复杂的四电子过程导致动力学缓慢,使得析氧半反应成为水裂解反应的瓶颈.长久以来,贵金属Ir和Ru基材料是被广泛研究的高活性的析氧催化剂.然而高成本和低储量极大地限制了它们的大规模工业化应用.因此,开发高效、储量丰富的析氧催化剂,意义重大但仍充满挑战性.本文考察了一种简便而有效的合成策略,在碱性水溶液条件下,成功实现将一系列Fe基金属有机框架(MOF)前驱物原位转化为无定形Fe基双金属氢氧化物纳米结构.这些由MOF前驱物转化得到的氢氧化物纳米结构保留了前驱体纳米棒的宏观形貌,由许多超细的无定形纳米颗粒(平均粒径小于10 nm)构成,在催化反应中可以提供丰富的催化活性位,相邻的纳米颗粒之间紧密接触,有利于电子在催化活性位之间传递.以玻碳电极作为基底,通过组分优化得到的NiFe-OH-0.75催化剂样品在电催化析氧反应中仅需270 mV的过电位便可达到10 mA cm^-2的电流密度,Tafel斜率为39 mV dec^-1.将催化剂负载到三维泡沫镍基底上时,由于电极基底导电性提升以及传质增加,在10 mA cm^?2的电流密度所需的过电位可以降低到235 mV,Tafel斜率为37 mV dec^?1,并且表现出较好的稳定性.同时,本文进一步证实这些无定形氢氧化物可以用作助催化剂,与合适的光敏剂结合,实现有效的光催化水氧化反应.在KH2PO4-K2HPO4缓冲溶液(pH=9)体系中,以Ru(2,2’-bipyridine)3]Cl₂为光敏剂,Na2S2O8为电子受体,由CoFe-MIL-0.75前驱体转化所得到的CoFe-OH-0.75助催化剂表现出更优越的光催化产氧性能,产氧效率可达59.6%.本文结果可以为其他基于MOF及其相关衍生材料的制备提供新思路.

In situ formation of amorphous Fe-based bimetallic hydroxides from metal-organic frameworks as efficient oxygen evolution catalysts

Oxygen evolution from water driven by electrocatalysis or photocatalysis poses a significant chal-lenge as it requires the use of efficient electro-/photo-catalysts to drive the four-electron oxygen evolution reaction (OER). Herein, we report the development of an effective strategy for the in situ chemical transformation of Fe-based bimetallic MIL-88 metal-organic frameworks (MOFs) into corresponding bimetallic hydroxides, which are composed of amorphous ultrasmall nanoparticles and afford an abundance of catalytically active sites. Optimized MOF-derived NiFe-OH-0.75 catalyst coated on glassy carbon electrodes achieved a current density of 10 mA cm-2 in the electrocatalytic OER with a small overpotential of 270 mV, which could be decreased to 235 mV when loading the catalysts on a nickel foam substrate. Moreover, these MOF-derived Fe-based bimetallic hydroxides can be used as efficient cocatalysts when combined with suitable photosensitizers for photocatalytic water oxidation.