Carbon-Armored Co₉S₈ Nanoparticles as All-pH Efficient and Durable H₂-Evolving Electrocatalysts

Abstract

Splitting water to produce hydrogen requires the development of non-noble-metal catalysts that are able to make this reaction feasible and energy efficient. Herein, we show that cobalt pentlandite (Co9S8) nanoparticles can serve as an electrochemically active, noble-metal-free material toward hydrogen evolution reaction, and they work stably in neutral solution (pH 7) but not in acidic (pH 0) and basic (pH 14) media. We, therefore, further present a carbon-armoring strategy to increase the durability and activity of Co9S8 over a wider pH range. In particular, carbon-armored Co9S8 nanoparticles (Co9S8@C) are prepared by direct thermal treatment of a mixture of cobalt nitrate and trithiocyanuric acid at 700 °C in N2 atmosphere. Trithiocyanuric acid functions as both sulfur and carbon sources in the reaction system. The resulting Co9S8@C material operates well with high activity over a broad pH range, from pH 0 to 14, and gives nearly 100% Faradaic yield during hydrogen evolution reaction under acidic (pH 0), neutral (pH 7), and basic (pH 14) media. To the best of our knowledge, this is the first time that a transition-metal chalcogenide material is shown to have all-pH efficient and durable electrocatalytic activity. Identifying Co9S8 as the catalytically active phase and developing carbon-armoring as the improvement strategy are anticipated to give a fresh impetus to rational design of high-performance noble-metal-free water splitting catalysts.

Hollow TiO2@Co9S8 Core–Branch Arrays as Bifunctional Electrocatalysts for Efficient Oxygen/Hydrogen Production

“…The electrochemical impedance spectroscopy were conducted at the polarization voltage corresponding to current density of 10 mA cm −2 , in a frequency range from 100 kHz to 50 mHz with an AC amplitude of 10 mV. The stability test was carried out at different constant current densities (10,30, and 50 mA cm −2 ) for 10 h each.…”

Encapsulation of CoSx Nanocrystals into N/S Co‐Doped Honeycomb‐Like 3D Porous Carbon for High‐Performance Lithium Storage

“…It is well known that the so‐called D band is associated with amorphous carbon, where defects or edges can break the symmetry and selection rule,37 and G band is assigned to the E 2g vibrations of graphite 38, 39. The strong D band indicates that lots of disordered sites, heteroatom doping, or defects were existing in the carbon structure of PC and CS@PC 40. The peak intensity of I D / I G generally provides a useful index about the degree of crystallinity of carbon materials, that is, the bigger the I D / I G ratio, the higher the degree of disordering in the carbon material 41.…”

“…The peak intensity of I D / I G generally provides a useful index about the degree of crystallinity of carbon materials, that is, the bigger the I D / I G ratio, the higher the degree of disordering in the carbon material 41. The I D / I G values of PC and CS@PC are 1.29 and 1.22, respectively, indicating the carbon in both samples have low crystallinity, which is caused by nitrogen and sulfur co‐doping 40. The incorporation of nitrogen and sulfur into carbon can increase the conductivity of the material and thus improve its electrochemical performance.…”

“…The high‐resolution spectrum of Co 2p (Figure 4b) displays four main peaks: two peaks centered around binding energies 778.9 and 793.8 eV are attributed to the Co—S bond and two peaks at 781.6 and 797.8 eV belong to the Co—O bond 16, 45. The oxygen element in the CS@PC composite may arise from three parts: the absorbed hydroxide species, precursor residual oxygen after vulcanization, and sulfur species from partial oxidation of material surface 40, 46, 47. Besides, the two satellite peaks at 785.3 and 803.1 eV could be indexed to the shake‐up peak of Co 2+ 16.…”

Facile Synthesis of Mo2C Nanocrystals Embedded in Nanoporous Carbon Network for Efficient Hydrogen Evolution

“…The stability of Mo 2 C@C was assessed by long-term chronopotential recording. [55,56] As shown in Figure 4d, Mo 2 C@C only exhibited a slight increase in the overpotential and its morphology was well maintained ( Figure S4) after 10000 s of measurement, indicating its satisfactory stability. We further investigated the HER performance of Mo 2 C@C in acidic (0.5 mol/L H 2 SO 4 ) and neutral media (1.0 mol/L PBS).…”