铁取代的钴-磷多酸作为酸性介质中性能增强的析氧催化剂

纯无机的非贵金属基双/三金属氢氧(氧)化物因其优异的析氧反应(OER)性能而得到广泛关注及研究.但这些催化剂的原子精度的结构表征较为困难,阻碍了人们对其构效关系的认识,从而影响了进一步对催化性能的精确调控.金属有机框架(MOFs)材料因具有明确的结构及化学组成可调等优点,可以作为一类结构确定的OER电催化剂,但是MOFs为有机配体和金属离子配位形成的框架材料,与金属氢氧(氧)化物结构类型不同.多酸是由高氧化态的Mo^Ⅵ/Ⅴ,W^Ⅵ/Ⅴ,V^Ⅴ/Ⅳ,Nb^Ⅴ和Ta^Ⅴ等组成的金属-氧簇.多酸尺寸介于分子与块体氧化物之间,可以被看作一种具有明确结构的分子氧化物.因此,多酸可用作模型体系从分子水平上探究金属氢氧(氧)化物催化剂的反应机理.此外,多酸已被证明是很有前景的非贵金属水氧化催化剂.对于OER,酸性介质更具优势,因为它与碱性介质相比具有高能效、低欧姆损耗、易于产物分离等优点.但是,非贵金属OER电催化剂在酸性介质中很难稳定且性能通常不如贵金属催化剂.制备酸性介质中高效和稳定的非贵金属OER电催化剂仍然是一大挑战.在本论文中,我们首先采用'原位同构取代'策略,将结构明确的[{Co4(OH)3PO4}4(SiW9O34)4]^32-(1)钴-磷多酸阴离子中的Co原子替换成Fe原子,合成了不同Fe含量的[{Fe2Co2(OH)3PO4}4(SiW9O34)4]^24-(2)和[{FeCo3(OH)3PO4}4(SiW9O34)4]^28-(3).然后通过离子交换,向1,2和3中引入Ba^2+,成功合成了不溶于水的多酸阴离子结构维持的多相催化剂Ba[1],Ba[2]和Ba[3].性能最好的Ba[3]在0.5 mol L^-1 H2SO4溶液中达到10 mA cm^-2的电流密度仅需要385 mV过电位(无iR校正),比相同条件下无Fe取代的Ba[1]和商业IrO2催化剂的过电位分别低66 mV和8 mV.经过2000圈的循环伏安测试和24 h的长时间电解测试,Ba[1],Ba[2]和Ba[3]均表现出较高的稳定性.另外,采用红外光谱(FT-IR)以及电感耦合等离子体质谱(ICP-MS)等多种表征测试手段进一步确认了它们的稳定性.本文采用的'原位同构取代'策略为合成更高效的结构明确的多金属催化剂提供了新思路,同时也为进一步从分子水平上探索相关催化机理提供了难得的模型.

Fe-substituted cobalt-phosphate polyoxometalates as enhanced oxygen evolution catalysts in acidic media

All-inorganic and earth-abundant bi-/trimetallic hydr(oxy)oxides are widely used as oxygen evolution electrocatalysts owing to their remarkable performance.However,their atomically precise structures remain undefined,complicating their optimization and limiting the understanding of their enhanced performance.Here,the underlying structure-property correlation is explored by using a well-defined cobalt-phosphate polyoxometalate cluster [{(Co4)(OH)3(PO4)}4(SiW9 O34)4]^32-(1),which may serve as a molecular model of multimetal hydr(oxy)oxides.The catalytic activity is enhanced upon replacing Co by Fe in 1,resulting in a reduced overpotential(385 mV) for oxygen evolution(by 66 mV) compared to that of the parent 1 at 10 mA cm^-2 in an acidic medium;this overpotential is comparable to that for the IrO2 catalyst These abundant-metal-based polyoxometalates exhibit high stability,with no evidence of degradation even after 24 h of operation.