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Exploring highly efficient and low cost bifunctional electrocatalysts for overall water splitting is of primary importance for renewable energy storage. Here, a novel amorphous CoFeO x (OH) y /CoO x (OH) y nanosphere (CFOH/COH) with unique core/shell structure was produced through a simple one-step solvothermal reaction, which exhibited enhanced activity for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) across the water splitting process. Benefited from the unique core/shell character, the amorphous structure as well as the amorphous interface, the active sites of CFOH/COH were well optimized, thus finally leading to the activity enhancement. The CFOH/COH-1 catalyst (with the Co/Fe ratio of about 1) displayed the best performance among the tested catalysts, exhibiting the overpotentials of 0.324 V and 0.263 V to achieve the current density of 10 mA cm−2 for OER and HER in 1.0 M KOH solution, respectively, smaller than those of pure Fe- or Co-based amorphous catalysts. Furthermore, the CFOH/COH-1 exhibited robust catalytic activity with a voltage of 1.59 V to reach a current density of 10 mA cm−2, when adopted as the bifunctional catalyst for full water splitting. This work highlights the important role of amorphous transition metal based heterostructure for boosting the HER and OER performance. CFOH/COH core/shell structure with amorphous interface has been produced via the simple one-step solvothermal reaction successfully. Benefited from the optimization of active sites, the CFOH/COH exhibited advanced electrocatalytic activity for overall water splitting. Image 1 [ABSTRACT FROM AUTHOR]

Developing efficient and non-noble metal electrocatalysts for oxygen evolution reaction (OER) at lower overpotential has been considered as a clean and effective strategy for replacing fossil feedstocks. Transitional metal oxides (TMO) electrocatalysts have been actively pursued because of their low-cost and strong stability in alkaline. However, the efficiency for most of developed TMO has been refrained by poor intrinsic electrical conductivity and exposed active sites. Herein, we demonstrate a sulfur incorporation strategy to accomplish greatly optimized OER performance in CoFe 2 O 4 /MWCNT (S-CFO/MWCNT) nanocomposite. Sulfur incorporation into CoFe 2 O 4 not only brings about more active sites in CFO frameworks, but also retains the pristine stable inverse spinel crystal structure which renders the high durability of the S-CFO/MWCNT catalyst. Specifically, the electrocatalysts exhibited greatly optimized OER catalytic activity with overpotential of about 0.36 V achieving current density of about 10 mA cm −2 and Tafel slope of about 43 mV dec −1 , together with stronger stability. Our work demonstrates an effective way to pursue highly efficient OER electrocatalysts. [ABSTRACT FROM AUTHOR]