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⁺(O_h)–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⁺(O_h)–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⁺(O_h) 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.

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。