A Simple Electrochemical Route to Access Amorphous Mixed‐Metal Hydroxides for Supercapacitor Electrode Materials

Abstract

mixed-metal hydroxide compounds such as Ni-Al, [ 3 ] Co-Ni, [4][5][6][7][8][9][10] Mn-Co, [ 11 ] Co-Ru, [ 12 ] Ni-Co-Cu, [ 13 ] and Ni-Co-Zn [ 14 ] have advantages over single-composition compounds as positive electrode materials for supercapacitors because mixed-metal compounds greatly promote the integrated electrochemical performance. [15][16][17][18] Almost all efforts in this fi eld have been directed towards crystalline mixed-metal hydroxide materials because these compounds have superior electrochemical performance with high specifi c capacitance, excellent rate capability, high energy density, and high power density. [4][5][6][7][8][9][10]19,20 ] However, supercapacitors made from crystalline compounds usually exhibit a very poor or short cycle life, [4][5][6][7][8][9][10] which makes their practical use limited. Typically, the cycling stability of a Ni(OH) 2 -Co(OH) 2 -graphene asymmetric supercapacitor shows a 70% retention after 1000 cycles. [ 8 ] Therefore, increasing the cycle life of mixed-metal hydroxide materials is a signifi cant challenge in supercapacitor applications.Although most positive electrode materials are based on crystalline mixed-metal hydroxides high activities can also be achieved with amorphous phases. It has been shown that the integrated electrochemical performance of amorphous metal hydroxides, such as Ni(OH) 2 and Co(OH) 2 , is commensurate with the crystallinity of the materials in the supercapacitor. [ 21,22 ] Considering the excellent electrochemical performance of crystalline mixed-metal hydroxide electrodes several benefi ts should be realizable by the development of amorphous mixed-metal hydroxide electrodes. However, commonly used methods for the production of amorphous oxide materials are not typically amenable to amorphous mixed-metal hydroxides. [ 18 ] We thus present a simple, facile, and chemically clean electrochemical method (experimental details in the Experimental Section and in Supporting Information S1) to prepare amorphous phases of mixed-metal hydroxides. They exhibited excellent performances as positive supercapacitor electrodes and a fabricated device showed a long-term cycling stability characterized by 94% retention after 20 000 cycles. This proof-of-principle investigation using amorphous mixed-metal hydroxides (amorphous Ni-Co-Fe hydroxide) demonstrates the broad applicability Supercapacitors or electrochemical capacitors, as energy storage devices, require very stable positive electrode materials for useful applications. Although most positive electrodes are based on crystalline mixed-metal hydroxides, their pseudocapacitors usually perform poorly or have a short cycle life. High activities can be achieved with amorphous phases. Methods to produce amorphous materials are also not typically amenable towards mixed-metal compositions. It is demonstrated that electrochemistry in an ambient environment can be used to produce a series of amorphous mixedmetal hydroxides with a homogeneous distribution of metals for use as positive electrode materials in a s...

High capacitive amorphous barium nickel phosphate nanofibers for electrochemical energy storage

“…Moreover amorphous material possesses much more unsaturated ligand atoms and efficient electrochemically active sites compared to crystalline counterpart. 52 These features favour the charge transport process in the material. This is conrmed by the low interface charge transfer resistance and good rate ability of the Ba x Ni 3Àx (PO 4 ) 2 material shown above.…”

“…Similar phenomenon has been reported by Li et al who found superior supercapacitive performance with a series of amorphous Ni-Co-Fe hydroxides. 52 It is ascribed to the unique nature of amorphous materials which is disorder in long-range but is structurally order in short-range. Moreover amorphous material possesses much more unsaturated ligand atoms and efficient electrochemically active sites compared to crystalline counterpart.…”

Two-Dimensional, Porous Nickel–Cobalt Sulfide for High-Performance Asymmetric Supercapacitors

“…Besides, crystallinity also plays an important role that amorphous electrochemically active materials usually possess better cycling stability because activation process is needed at the first several hundreds of cycles. 28 Amorphous structure can also endure the large structural changes during redox reactions well, leading to better cycling stability. Then, the effects of self-doping and crystallinity are optimized through changing the vulcanizing time.…”

Integration of nickel–cobalt double hydroxide nanosheets and polypyrrole films with functionalized partially exfoliated graphite for asymmetric supercapacitors with improved rate capability

“…[1][2][3][4][5][6][7] Furthermore, pseudocapacitive properties may be improved through coincorporation of Ni and Co in the hydroxides to form Ni-Co double hydroxides, due to the possible valence interchange or charge hopping between Ni and Co cations. [1][2][3][4][5][6][7] Furthermore, pseudocapacitive properties may be improved through coincorporation of Ni and Co in the hydroxides to form Ni-Co double hydroxides, due to the possible valence interchange or charge hopping between Ni and Co cations.…”

“…1,4,6,[10][11][19][20] However, the specific Please do not adjust margins Please do not adjust margins capacitance of the ASCs will be restricted due to the limited specific capacitance of carbon anodes which store charges mainly through electric double layer. So asymmetric supercapacitors (ASCs) were usually assembled for nickel and cobalt hydroxides based materials to broaden their cell voltages.…”