Co₉S₈‐Catalyzed Growth of Thin‐Walled Graphite Microtubes for Robust, Efficient Overall Water Splitting

Abstract

Co9S8 crystals can catalyze the growth of thin‐walled graphite microtubes (GMTs) through a catalytic chemical vapor deposition (CCVD) process using thiourea as the precursor. The growth of GMTs follows a tip‐growth mechanism with tube diameters up to a few micrometer. The hollow interiors of the GMTs are filled with carbon nanotubes and wrinkled graphene layers, which form a unique nanotube/graphene‐in‐microtube structure. As‐formed GMTs are N,S‐codoped with lots of Co9S8 nanoparticles encapsulated in their inner walls. These GMTs are room‐temperature ferromagnets and can be loaded on Ni foams to work as binder‐free electrocatalysts with low overpotential (310 mV at 50 mA cm−2 for the oxygen evolution reaction (OER) and 284 mV at 50 mA cm−2 for the hydrogen evolution reaction (HER)) and long‐term durability (continuous work for 120 h without loss in performance). Our research proves that metal sulfides can catalyze the growth of graphite microtubes and as‐formed GMTs may potentially be used as functional building blocks to construct new kinds of electrochemical devices for various energy‐related applications.

Cobalt‐Vanadium Hydroxide Nanoneedles with a Free‐Standing Structure as High‐Performance Oxygen Evolution Reaction Electrocatalysts

“…Remarkably, the Co 0.75 V 0.25 ‐HNNs exhibit the best OER activity with only 266 and 350 mV needed to drive the current densities of 10 and 100 mA cm −2 (Figures a&b), respectively. To our best knowledge, this is the first report on freestanding CoV‐hydroxide nanoneedles as OER catalysts with such low overpotential at the benchmark current density, which is comparable to most of the reported Co‐based and V‐based catalysts, such as hydroxide/ oxyhydroxide,,,, oxide,, chalcogenide, and phosphide ,,. As shown in partially amplified Figure a (Figure S6), the two anodic peaks at 1.2∼1.5 V versus RHE observed for NF@Co‐HNNs are associated with the oxidation of Co 2+ to Co 3+ and Co 3+ to Co 4+ , respectively ,,.…”

Ultrathinning Nickel Sulfide with Modulated Electron Density for Efficient Water Splitting

“…[38] Despite prominent progress that has been made, most research on nickel sulfide-based catalysts concentrated on only one of the above motioned strategies, and thus their catalytic performance was still far from satisfactory. [39][40][41] Additionally, the available synthesis procedures for these catalysts with improved catalytic performance by increasing active site density or optimizing the intrinsic activity usually involved multisteps and undesired sulfidation process with poisonous sulfurcontaining gas. In this regard, developing a cost-effective and scalable method for the integration of both morphology engineering and electronic modulation to maximize the catalytic performance of nickel sulfides is highly demanded but remains a significant challenge to date.…”

Graphene‐Encapsulated Co9S8 Nanoparticles on N,S‐Codoped Carbon Nanotubes: An Efficient Bifunctional Oxygen Electrocatalyst

“…[39] After carefully comparing the SEM and TEM images, XRD patterns,E DS data, and XPS data of Co/S/N-800 before anda fter acid treatment ( Figure S10 in the Supporting Information), we can conclude that nearly all Co 9 S 8 nanoparticles have disappeared. [39] After carefully comparing the SEM and TEM images, XRD patterns,E DS data, and XPS data of Co/S/N-800 before anda fter acid treatment ( Figure S10 in the Supporting Information), we can conclude that nearly all Co 9 S 8 nanoparticles have disappeared.…”

“…First, the Co 9 S 8 nanoparticles in Co/N-C-800 were dissolved by using concentrated HNO 3 . [39] After carefully comparing the SEM and TEM images, XRD patterns,E DS data, and XPS data of Co/S/N-800 before anda fter acid treatment ( Figure S10 in the Supporting Information), we can conclude that nearly all Co 9 S 8 nanoparticles have disappeared. The corresponding LSV curves show that, after acid treatment, the OER potential (at j = 10 mA cm À2 )s harply increases to 1.781 Vf rom the initial 1.591 V( Figure S11a in the Supporting Information), but E 1/2 for the ORR only drops by 9mV( Figure S11b in the Supporting Information).…”