Controlled Phase Evolution from Co Nanochains to CoO Nanocubes and Their Application as OER Catalysts

Abstract

One-dimensional materials favoring efficient charge transfer have attracted enormous attentions. Here cobalt nanochains are prepared by a direct-current (DC) arc-discharge method under the gaseous mixture of He and H 2 . The Co nanochains can range up to several micrometers. When H 2 is replaced by CO 2 , the sample shows a phase evolution from Co nanochains to CoO nanocubes. The ratio of CoO/Co can be effortlessly altered by varying the partial pressure of CO 2 in the reaction gas mixture. CoO nanocubes are attained in the pure CO 2 . The prepared samples are explored as catalyst for oxygen evolution reaction (OER). The catalytic activity is highly dependent on the phase proportion of Co and CoO. The sample prepared under CO 2 :He = 1:7 unveils the optimal OER performance with an onset point of 1.50 V versus reversible hydrogen electrode (RHE) and an overpotential of 350 mV at 10 mA cm −2 . The high OER performance can be attributed to synergistic effect and charge transfer process between Co and CoO. Co can inject electrons into CoO, which manipulates the work function of CoO to make it more suitable for oxygen evolution. The good OER performance can also be ascribed to the defective structure of CoO. The CoO/Co composite shows good robustness with less than 8% current loss throughout the long-term test.

Recent Development of Ni/Fe‐Based Micro/Nanostructures toward Photo/Electrochemical Water Oxidation

“…However, water oxidation to O 2 is also one of the intriguing objectives for developing efficient water‐splitting photocatalysts 61. Oxygen evolution catalysts (OECs) based on earth‐abundant elements such as MnO x ,62 CoO x ,63 FeO x ,64 and NiO x 65 have been well investigated owing to their high catalytic activity in recent years.…”

NiFe-based nanostructures on nickel foam as highly efficiently electrocatalysts for oxygen and hydrogen evolution reactions

“…Nevertheless, their scarcity and high cost hinder the large-scale deployment. Recently, transition metal compounds came into view with the advantage of low cost and high activity for OER including MnO [76,77] , FeO [78,79] , CoO [80,81] and NiO [82,83] . Some of them were coated on nickel foam to enhance the OER performance and high stability [60,84,85] .…”

Oxygen Evolution Activity of Co–Ni Nanochain Alloys: Promotion by Electron Injection

“…The surface of the nanochains can be partially oxidized upon exposure to air or under electrochemical oxidation, giving core–shell structures. According to our previous studies on metal core and metal oxide shell structures, the metal cores are able to inject electrons into oxide layers, manipulating the work function of the oxide and improving the efficiency of oxygen evolution . Co–Ni alloy nanochains thus show high activity for OER.…”

“…Synthesis of Co nanochains and Ni nanochains . The Co nanochains were produced by a direct current (DC) arc‐discharge method as reported in our previous works . 8 mm Cobalt and pure graphite rods were used as anode and cathode, respectively.…”