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Filling the oxygen vacancies in Co3O4 with phosphorus: an ultra-efficient electrocatalyst for overall water splitting†
Energy & Environmental Science ( IF 32.4 ) Pub Date : 2017-10-17 00:00:00 , DOI: 10.1039/c7ee01917c
Zhaohui Xiao,Yu Wang,Yu-Cheng Huang,Zengxi Wei,Chung-Li Dong,Jianmin Ma,Shaohua Shen,Yafei Li,Shuangyin Wang

It is of essential importance to design an electrocatalyst with excellent performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting. Co3O4 has been developed as a highly efficient OER electrocatalyst, but it has almost no activity for HER. In a previous study, it has been demonstrated that the formation of oxygen vacancies (VO) in Co3O4 can significantly enhance the OER activity. However, the stability of VO needs to be considered, especially under the highly oxidizing conditions of the OER process. It is a big challenge to stabilize the VO in Co3O4 while reserving the excellent activity. Filling the oxygen vacancies with heteroatoms in the VO-rich Co3O4 may be a smart strategy to stabilize the VO by compensating the coordination numbers and obtain an even surprising activity due to the modification of electronic properties by heteroatoms. Herein, we successfully transformed VO-rich Co3O4 into an HER-OER electrocatalyst by filling the in situ formed VO in Co3O4 with phosphorus (P-Co3O4) by treating Co3O4 with Ar plasma in the presence of a P precursor. The relatively lower coordination numbers in VO-Co3O4 than those in pristine Co3O4 were evidenced by X-ray adsorption spectroscopy, indicating that the oxygen vacancies were created after Ar plasma etching. On the other hand, the relatively higher coordination numbers in P-Co3O4 than those in VO-Co3O4 and nearly same coordination number as that in pristine Co3O4 strongly suggest the efficient filling of P in the vacancies by treatment with Ar plasma in the presence of a P precursor. The Co–O bonds in Co3O4 consist of octahedral Co3+(Oh)–O and tetrahedral Co2+(Td)–O (Oh, octahedral coordination by six oxygen atoms and Td, tetrahedral coordination by four oxygen atoms). More Co3+(Oh)–O are broken when oxygen vacancies are formed in VO-Co3O4, and more electrons enter the octahedral Co 3d orbital than those entering the tetrahedral Co 3d orbital. Then, with the filling of P in the vacancy site, electrons are transferred out of the Co 3d states, and more Co2+(Td) than Co3+(Oh) are left in P-Co3O4. These results suggest that the favored catalytic ability of P-Co3O4 is dominated by the Co2+(Td) site. P-Co3O4 shows superior electrocatalytic activities for HER and OER (among the best non-precious metal catalysts). Owing to its superior efficiency, P-Co3O4 can directly catalyze overall water splitting with excellent performance. The theoretical calculations illustrated that the improved electrical conductivity and intermediate binding by P-filling contributed significantly to the enhanced HER and OER activity of Co3O4.

中文翻译:

用磷 填充Co 3 O 4中的氧空位:一种用于整体水分解的超高效电催化剂

设计一种对于水分解过程中的析氢反应(HER)和析氧反应(OER)均具有优异性能的电催化剂至关重要。Co 3 O 4已被开发为一种高效的OER电催化剂,但对HER几乎没有活性。在先前的研究中,已经证明在Co 3 O 4中形成氧空位(V O)可以显着增强OER活性。但是,需要考虑V O的稳定性,特别是在OER工艺的高度氧化条件下。稳定Co 3 O 4中的V O是一个巨大的挑战同时保留出色的活动。在富V O的Co 3 O 4中用杂原子填充氧空位可能是一种聪明的策略,可以通过补偿配位数来稳定V O,并且由于杂原子对电子性质的改变而获得了令人惊讶的活性。在这里,我们通过处理Co 3 O 4,用磷(P-Co 3 O 4)填充了Co 3 O 4中原位形成的V O,成功地将富含V O的Co 3 O 4转化为HER-OER电催化剂。在P前驱体存在下用Ar等离子体处理。X射线吸收光谱法证明,V O -Co 3 O 4中的配位数比原始Co 3 O 4中的配位数低,这表明在Ar等离子刻蚀后产生了氧空位。另一方面,P-Co 3 O 4中的配位数比V O -Co 3 O 4中的配位数高,并且与原始Co 3 O 4的配位数几乎相同。强烈建议通过在P前体存在下用Ar等离子体处理有效地填充空位中的P。Co 3 O 4中的Co-O键由八面体Co 3+(O h)-O和四面体Co 2+(T d)-O(Oh,八面体由六个氧原子组成,T d,四面体由四个氧原子组成)组成氧原子)。当V O -Co 3 O 4中形成氧空位时,更多的Co 3+(O h)–O被破坏,进入八面体Co 3d轨道的电子比进入四面体Co 3d轨道的电子更多。然后,通过在空位中填充P,电子从Co 3d态转移出,并且在P-Co 3 O 4中留下的Co 2+(T d)比Co 3+(O h)多。这些结果表明,P-Co 3 O 4的有利催化能力主要由Co 2+(T d)位点决定。P-Co 3 O 4对HER和OER(在最好的非贵金属催化剂中)显示出优异的电催化活性。由于其卓越的效率,P-Co 3O 4具有优异的性能,可直接催化整体水分解。理论计算表明,通过P填充提高电导率和中间键合可以显着提高Co 3 O 4的HER和OER活性。
更新日期:2017-10-17
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