Filling the oxygen vacancies in Co3O4 with phosphorus: an ultra-efficient electrocatalyst for overall water splitting

Author(s): Zhaohui Xiao ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Yu Wang ⁶ ^, ⁷ ^, ⁸ ^, ⁵ , Yu-Cheng Huang ⁹ ^, ¹⁰ ^, ¹¹ , Zengxi Wei ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Chung-Li Dong ¹² ^, ¹³ ^, ¹⁴ ^, ¹¹ , Jianmin Ma ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Shaohua Shen ¹⁵ ^, ¹⁶ ^, ¹⁷ ^, ⁵ , Yafei Li ⁶ ^, ⁷ ^, ⁸ ^, ⁵ , Shuangyin Wang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵

Publication date (Electronic): 2017

Journal: Energy & Environmental Science

Publisher: Royal Society of Chemistry (RSC)

Read this article at

ScienceOpenPublisher

Bookmark

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

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.

Abstract

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. Co ₃O ₄ 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 Co ₃O ₄ 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 Co ₃O ₄ while reserving the excellent activity. Filling the oxygen vacancies with heteroatoms in the V _O-rich Co ₃O ₄ 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 Co ₃O ₄ into an HER-OER electrocatalyst by filling the in situ formed V _O in Co ₃O ₄ with phosphorus (P-Co ₃O ₄) by treating Co ₃O ₄ with Ar plasma in the presence of a P precursor. The relatively lower coordination numbers in V _O-Co ₃O ₄ than those in pristine Co ₃O ₄ 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-Co ₃O ₄ than those in V _O-Co ₃O ₄ and nearly same coordination number as that in pristine Co ₃O ₄ 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 Co ₃O ₄ consist of octahedral Co ³⁺(O _h)–O and tetrahedral Co ²⁺(T _d)–O (Oh, octahedral coordination by six oxygen atoms and T _d, tetrahedral coordination by four oxygen atoms). More Co ³⁺(O _h)–O are broken when oxygen vacancies are formed in V _O-Co ₃O ₄, 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 Co ²⁺(T _d) than Co ³⁺(O _h) are left in P-Co ₃O ₄. These results suggest that the favored catalytic ability of P-Co ₃O ₄ is dominated by the Co ²⁺(T _d) site. P-Co ₃O ₄ shows superior electrocatalytic activities for HER and OER (among the best non-precious metal catalysts). Owing to its superior efficiency, P-Co ₃O ₄ 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 Co ₃O ₄.

Related collections

Most cited references 20

Record: found
Abstract: found
Article: not found

Defect Chemistry of Nonprecious-Metal Electrocatalysts for Oxygen Reactions.

Dafeng Yan, Yunxiao Li, Jia Huo … (2017)

Oxygen electrocatalysis, including the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER), is a critical process for metal-air batteries. Therefore, the development of electrocatalysts for the OER and the ORR is of essential importance. Indeed, various advanced electrocatalysts have been designed for the ORR or the OER; however, the origin of the advanced activity of oxygen electrocatalysts is still somewhat controversial. The enhanced activity is usually attributed to the high surface areas, the unique facet structures, the enhanced conductivities, or even to unclear synergistic effects, but the importance of the defects, especially the intrinsic defects, is often neglected. More recently, the important role of defects in oxygen electrocatalysis has been demonstrated by several groups. To make the defect effect clearer, the recent development of this concept is reviewed here and a novel principle for the design of oxygen electrocatalysts is proposed. An overview of the defects in carbon-based, metal-free electrocatalysts for ORR and various defects in metal oxides/selenides for OER is also provided. The types of defects and controllable strategies to generate defects in electrocatalysts are presented, along with techniques to identify the defects. The defect-activity relationship is also explored by theoretical methods.