Enhancing Oxygen Evolution Catalytic Performance of Nickel Borate with Cobalt Doping and Carbon Nanotubes

Abstract

Metal borates have recently been recognized as alternative earth-abundant water oxidation catalysts. Herein, we employed solid-state synthesis to prepare a series of NiÀ Co borates, Ni a Co (3-a) (BO 3 ) 2 , with a Kotoite structure to elucidate the effect of the metal-doping on the water oxidation activity of metal borates. We performed electrocatalytic and photocatalytic studies to reveal that the catalytic activity could be enhanced with cobalt doping and by using carbon nanotubes (CNTs) as the substrate. Ni 3 B 2 O 6 exhibits an overpotential of 525 mV to reach current densities of 10 mA cm À 2 in 1 M KOH solution, while it is 355 mV for Co 2 NiB 2 O 6 _CNT@CC. The overpotential is also 100 mV lower than the pure catalyst (Co 2 NiB 2 O 6 @CC, 445 mV). The as-prepared samples exhibit significantly enhanced photocatalytic activities for water oxidation under visible-light irradiation with an increasing cobalt ratio, and an average O 2 evolution rate of up to 1822 μmol h À 1 g À 1 is obtained for Co 3 B 2 O 6 , which is nearly 1.78, 4.25, and 4.90 times higher than the rates obtained for Co 2 NiB

A Mini Review on Borate Photocatalysts for Water Decomposition: Synthesis, Structure, and Further Challenges

“…The term "high temperature" is used in relation to the synthesis temperature of other soft chemical synthesis methods. The synthesis of borates by high-temperature solid-state method is relatively simple and effective, for example, K 3 Ta 3 B 2 O 12 [50,51], InBO 3 [52], Ga 4 B 2 O 9 [53], Cd 12 Ge 17 B 8 O 58 [54], CuB 2 O 4 [55], Cu 3 B 2 O 6 [55], PbGaBO 4 [56], and Ni a Co 3−a O 4 [49], can be prepared by this method. However, only thermodynamically stable phases can be obtained by this method, and kinetically stable phases cannot be obtained.…”

“…Furthermore, considering the cations in the borate photocatalysts, we note that the first transition metal borates have small bandgaps (≤3.3 eV), such as CuB 2 O 4 [55], Cu 3 B 2 O 6 [55], Co 3 B 2 O 6 [49], Co 2 NiB 2 O 6 [49], CoNi 2 B 2 O 6 [49], Ni 3 B 2 O 6 [49], Cu-borate-1 [59], and Cuborate-2, [49] most of which are capable of decomposing water under visible light or simulated sunlight. Others include p-block borates, and both the second and third transition metal borates have bandgaps greater than 4.0 eV.…”

“…Oxygen Evolution Half-Reaction (OEHR): OEHR is an aqueous solution that contains a photogenerated electron sacrificer, such as Ag + [47,48], Na 2 S 2 O 8 [49], so the photogenerated holes react mainly with water molecules in the aqueous solution to produce oxygen (see Equation ( 3)).…”

Crystal growth and cation order of Ni3−xCoxB2O6 oxyborates

“…Recently, oxyborates M 3 B 2 O 6 (where M are Co, Ni, Mn) have attracted great interest due to their potential use as anode materials for lithium-ion and sodium-ion battery cells. [1][2][3][4][5][6][7] There have been a number of studies which show oxyborate Ni 3 B 2 O 6 to be a highly promising anode material for sodiumion batteries. [1][2][3]6,7 These studies were carried out on ceramic samples.…”

“…[1][2][3][4][5][6][7] There have been a number of studies which show oxyborate Ni 3 B 2 O 6 to be a highly promising anode material for sodiumion batteries. [1][2][3]6,7 These studies were carried out on ceramic samples. The Ni 3 B 2 O 6 electrode is known to have a reversible capacity of 428.9 mA h g −1 at 200 mA g −1 .…”