## 3 Results  
The two-step environmental growth scheme of the Ni-Co sulfide nanosheet-nanotube on nickel foam is illustrated in Figure 1. Firstly, the NiCo\({}_{2}\)O\({}_{4}\) precursor was firstly grown directly on Ni foam via following facile hydrothermal method, which is one of the most cost effective, environmentally friendly, and easy approachable non-toxic scientific methods for synthesizing controllable different morphology. Then, we carried out a calcination treatment so that the NiCo\({}_{2}\)O\({}_{4}\) nanosheet-nanowire arrays on Ni foam can be converted hydrothermally to Ni-Co sulfide nanosheet-nanotube arrays counterparts by reacting with Na\({}_{2}\)S, which is from attribution to the anion-exchange reaction between O\({}^{2-}\) and S\({}^{2-}\). Figure 2 presents the XRD pattern of the successful preparation of Ni-Co sulfide. The pure NiCo\({}_{2}\)O\({}_{4}\) phase is observed in the pristine pattern, while after sulfurizing (anion-exchange) process, the final products can be indexed to mixture of Co\({}_{4}\)S\({}_{3}\) (JCPDS No. 42-1448, a = b = c = 9.387) and Ni\({}_{3}\)S\({}_{2}\) (JCPDS No. 44-1418, a = b = 5.745, c = 7.135), in which Co\({}_{4}\)S\({}_{3}\) can be readily indexed to the (311), (400), (422), (511) and (440) and Ni\({}_{3}\)S\({}_{2}\) can be indexed to the(101), (110), (021), (211), (213), (122), and (300). There are no other diffraction peaks, implying the full conversion of the precursor into Ni-Co sulfide during the hydrothermal process. XPS was performed to further confirm the prepared sample, while the well fitted spectra of Ni, Co, S (Figure S1) illustrates the successful anion-exchange reaction between O\({}^{2-}\) and S\({}^{2-}\). The Ni 2p and Co 2p spectra of Ni-Co sulfide (Figure S1a,b) are well fitted into Ni\({}^{2+}\), Ni\({}^{3+}\), Co\({}^{2+}\), and Co\({}^{3+}\) accompanied with shakeup satellite, respectively. While, S 2p spectra (Figure S1c) display strong peaks at 161.6 eV and 163 eV, which can be associated with S\({}^{2-}\) species in the composite and sulfur ions in low coordination at the surface [28]. Figure 1: Schematic **illustration** of the synthesis processes of Ni-Co sulfide nanosheet-nanotube arrays. Figure 2: XRD pattern of as prepared Ni-Co sulfide arrays supported on Ni foam. To better elucidate the morphology, representative SEM images were carried out from the samples are given in Figure 3. The morphology of pristine Ni-Co oxide structures shown in Figure 3a,b demonstrates that nickel foam substrate surface was uniformly covered with a layer of uniform active material. The magnified SEM images (Figure 3c,d) show that large-scale, high dense and aligned Ni-Co sulfide arrays are supported on nickel foam substrate. EDS mapping of Ni-Co oxide and Ni-Co sulfide as shown in Figure S2. To demonstrate the morphology characters of Ni-Co sulfide arrays on Ni foam, the sulfide pattern was treated by focus ion beam irradiation. In the Figure 3e, the nanotubes in left part of the sample are wiped out by the Ga ion irradiation and the nanosheets feature is clearly exposed out of the arrays. And obviously the nanotubes (blue arrow) still left are connected with the nanosheet (yellow arrow), proving the formation of nanosheet-nanotubes feature of Ni-Co sulfide. Figure 3: SEM images of (**a**,**b**) Ni-Co oxide, (**c**,**d**) Ni-Co sulfide, and (**e**) the Ni-Co sulfide partially treated by focus ion beam irradiation. The closely structural information and morphology of the Ni-Co sulfide were investigated by TEM in Figure 4. A full view of a single hierarchical porous Ni-Co sulfide nanosheet-nanotube array in Figure 4a apparently shows the array consists of nanosheet below and nanotubes epitaxial growth from the nanosheet. The SAED pattern in the Figure 4b demonstrates the polycrystalline nature of the Ni-Co sulfide nanowire, the well-defined diffraction rings can be readily indexed to the Co\({}_{3}\)S\({}_{4}\) (220), (222), (400), (422), (511), (440), (800), and Ni\({}_{3}\)S\({}_{2}\) (021), (202), (211), (122), respectively.