Filling the oxygen vacancies in Co3O4 with phosphorus: an ultra-efficient electrocatalyst for overall water splitting
Filling the oxygen vacancies in Co3O4 with phosphorus: an ultra-efficient electrocatalyst for overall water splitting
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DOI：
10.1039/c7ee01917c
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发表时间：
2017-12-01
影响因子：
32.5
通讯作者：
Wang, Shuangyin
中科院分区：
文献类型：
--
作者：
Xiao, Zhaohui;Wang, Yu;Wang, Shuangyin
设计一种同时具有优良析氢和析氧性能的电催化剂对水裂解反应具有重要意义。Co_3O_4是一种高效的OER电催化剂，但它对HER几乎没有活性，在以前的研究中，Co_3O_4中氧空位（V-O）的形成可以显著提高OER活性。然而，需要考虑V-O的稳定性，特别是在OER工艺的高氧化条件下。如何在保持Co_3O_4优良活性的同时，稳定Co_3O_4中的V-O键是一个很大的挑战。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，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修饰而获得甚至令人惊讶的活性。在此，我们成功地将富含V-O的Co 3 O 4转化为HER-OER电催化剂，通过在P前体的存在下用Ar等离子体处理Co 3 O 4，用磷（P-Co 3 O 4）填充Co 3 O 4中原位形成的V-O。X射线吸收光谱表明，V-O-Co 3 O 4中的配位数比纯Co 3 O 4中的配位数低，说明Ar等离子体刻蚀后产生了氧空位。另一方面，相对较高的配位数在P-Co_3 O_4比那些在V-O-Co_3 O_4和几乎相同的配位数在原始Co_3 O_4强烈建议，有效地填充P在空位中的处理与Ar等离子体在P前体的存在下。Co_3O_4中的Co-O键由八面体的Co ~（3+）（OH）-O和四面体的Co ~（2+）（T-d）-O组成（OH为六个氧原子的八面体配位，T-d为四个氧原子的四面体配位）。V-O-Co 3 O 4中氧空位的形成使更多的Co 3+（OH）-O断裂，使更多的电子进入八面体Co 3d轨道.然后，随着P在空位中的填充，电子从Co 3d态转移出来，并且在P-Co 3 O 4中留下比Co 3+（Oh）更多的Co 2+（T-d）。这些结果表明，P-Co_3 O_4的催化活性主要受Co ~（2+）（T-d）位的影响。P-Co 3 O 4对HER和OER具有上级电催化活性（在非贵金属催化剂中）。由于其上级效率，P-Co 3 O 4可以直接催化整体水裂解，具有优异的性能。理论计算结果表明，P填充提高了Co 3 O 4的导电性和中间体结合能力，从而显著提高了其HER和OER活性。
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 (V-O) in Co3O4 can significantly enhance the OER activity. However, the stability of V-O needs to be considered, especially under the highly oxidizing conditions of the OER process. It is a big challenge to stabilize the V-O in Co3O4 while reserving the excellent activity. Filling the oxygen vacancies with heteroatoms in the V-O-rich Co3O4 may be a smart strategy to stabilize the V-O by compensating the coordination numbers and obtain an even surprising activity due to the modification of electronic properties by heteroatoms. Herein, we successfully transformed V-O-rich Co3O4 into an HER-OER electrocatalyst by filling the in situ formed V-O 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 V-O-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 V-O-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+(T-d)-O (Oh, octahedral coordination by six oxygen atoms and T-d, tetrahedral coordination by four oxygen atoms). More Co3+(Oh)-O are broken when oxygen vacancies are formed in V-O-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+(T-d) than Co3+(Oh) are left in P-Co3O4. These results suggest that the favored catalytic ability of P-Co3O4 is dominated by the Co2+(T-d) 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.