M_xCo_3−xO₄ (M = Co, Mn, Fe) porous nanocages derived from metal–organic frameworks as efficient water oxidation catalysts

Abstract

The design and development of efficient and robust water oxidation catalysts based on earth-abundant elements are crucial for energy conversion and storage technology. Herein, we report Co3O4 porous nanocages derived from simple metal-organic frameworks by a simple self-assemble method and a low temperature anneal process. This method can synthesize MxCo3−xO4 (M = Co, Mn, Fe) porous nanocages materials and allow precise control of ratio of substituted metal in Co3O4 catalysts. These catalysts were investigated for photochemical, chemical-driven (cerium (IV)-driven) and electrochemical water oxidation, and they presented a superior activity for water oxidation. The high turnover frequency (TOF) of ∼3.2 × 10 -4 s -1 per Co atom was obtained under neutral pH using Co3O4 porous nanocages in photocatalytic water oxidation reaction, which is comparable with those of nanostructured Co3O4 clusters supported on mesoporous silica. Under cerium (IV)-driven water oxidation condition, a high TOF of ∼3.6 × 10 −3 s −1 per Co atom was achieved, which was the highest among those of other known reported cobalt oxides. The overpotential of Co3O4 porous nanocages for the electrochemical water oxidation (η = 0.42 V at 1 mA cm -2 ) is comparable to the reported overpotentials of catalysts based on cobalt. Multiple experimental results (e.g. XRD, TEM, HR-TEM and XPS) confirm that Co3O4 porous nanocages are highly stable. This study illustrates a guideline to the design and synthesis of inexpensive and highly active spinel catalysts for water oxidation. 6,40-46 Figure 1. Schematic representation of (a) polyhedral representation of Co 3 O 4 (b) ball-and-stick representation of Co 3 O 4 (c) ball-and-stick representation of Co 4 O 4 core in spinel Co 3 O 4 (d) Mn 4 CaO 5 in the photosystemⅡ-WOC. Turquoise: Co 3+ ; teal: Co 2+ ; red: O; violet: Mn; brown: Ca.

A facile conversion of a Ni/Fe coordination polymer to a robust electrocatalyst for the oxygen evolution reaction

“…Very recently, PBs were served as precursors to prepare nanoporous metal oxide materials, which exhibited promising water oxidation activity in both neutral and basic media. [41][42][43] Since PBs have three-dimensional open architecture, and taking account of the high activity of Ni/Fe composites, it would be worth addressing a detailed research on Ni hexacyanoferrates (NiHCF) as new efficient OER catalyst.…”

Co/Cu-MFF derived mesoporous ternary metal oxide microcubes for enhancing the catalytic activity of the CO oxidation reaction

“…3a) constructed with two main peaks centering at about 779.5 and 794.6 eV, corresponding to the Co2p 3/2 and Co2p 1/2 respectively. 37,50,51 The relative percentage of Co 3+ and Co 2+ was calculated through the tted curves of Cu x Co 3Àx O 4 , and was plotted as functions of the Cu/Co atomic ratio in the solution of preparing precursors (Fig. 3b).…”

“…[30][31][32][33] Owing to its adjustable cavities and exible structures, various metal oxides with specic morphologies and interconnected pores have been fabricated by thermal decomposition of MOFs under suitable calcination conditions, expecting to improve their performance in specic applications. [34][35][36][37][38][39][40][41][42] Among them, ternary metal oxides have gained increasing considerations due to the structure merits and synergetic effect of multiple components. Therefore, bimetallic organic frameworks are considered highly desirable to facile synthesis of the ternary metal oxides.…”

MOFs for Electrocatalysis: From Serendipity to Design Strategies

“…In another instance, a series of Fe and Ni‐based MOFs are oxidatively transformed into Fe x Ni x –oxides, predominantly with spinel NiFe 2 O 4 structure, which display composition‐dependent OER activity in 0.1 m KOH . Likewise, the thermal synthesis of M x Co 3‐ x O 4 (M = Co, Mn, Fe) porous nanocage materials was reported by precisely controlling the composition of metals in Prussian blue analogues, M 3 [Co (CN) 6 ] 2 (M = Co, Mn, Fe) . Further, on‐site mild oxidation of metal centers into atomically dispersed metal oxide species is also perceived to induce OER activity in MOF‐derived structures.…”