Porous Co₉S₈/Nitrogen, Sulfur-Doped Carbon@Mo₂C Dual Catalyst for Efficient Water Splitting

Abstract

The exploration of highly efficient and stable bifunctional electrocatalysts for overall water splitting is currently of extreme interest for the efficient conversion of sustainable energy sources. Herein, we provide an earth-abundant, low-cost, and highly efficient bifunctional electrocatalyst composed of cobalt sulfide (CoS) and molybdenum carbide (MoC) nanoparticles anchored to metal-organic frameworks (MOFs)-derived nitrogen, sulfur-codoped graphitic carbon (CoS-NSC@MoC). The new composite mode of the electrocatalyst was realized through simple pyrolysis processes. The composite electrocatalyst shows outstanding hydrogen evolution reaction (HER) performance and excellent stability over the entire pH range. For example, it has a lower overpotential of 74, 89, and 121 mV with the Tafel slopes of 69.3, 86.7, and 106.4 mV dec to achieve a current density of 10 mA cm in 0.5 M HSO, 1.0 M KOH, and 1.0 M phosphate-buffered saline solutions, respectively. Moreover, it shows a small overpotential of 293 mV with a Tafel slope of 59.7 mV dec to reach 10 mA cm for the oxygen evolution reaction (OER) in 1.0 M KOH. The significantly enhanced HER and OER activities of CoS-NSC@MoC are mainly attributable to the electron transfer from Co to MoC, resulting in a lower Mo valence and a higher Co valence in CoS-NSC@MoC. Furthermore, using the CoS-NSC@MoC bifunctional electrocatalyst as both the anode for the OER and the cathode for the HER for overall water splitting, a cell voltage of only 1.61 V is needed to derive a current density of 10 mA cm. This interesting work offers a general method for designing and fabricating highly efficient and stable non-noble electrocatalysts for promising energy conversion.

Nitrogen and Sulfur Co‐Doped Mesoporous Carbon Embedded with Co9S8 Nanoparticles: Efficient Electrocatalysts for Hydrogen Evolution

“…The lower Tafel slope indicates the faster kinetics process . As exhibited in Figure b, the commercially available Pt/C possesses the lowest Tafel slope of 32.8 mV dec −1 , which is consistent with the reported results . GTCo900 also shows a low Tafel slope of 47.3 mV dec −1 , which is much lower than those of GTCo800 (109.4 mV dec −1 ) and GTCo1000 (59.1 mV dec −1 ).…”

“…[50] As exhibited in Figure 5b, the commercially available Pt/C possesses the lowest Tafel slope of 32.8 mV dec À 1 , which is consistent with the reported results. [16][17][18][19][20] GTCo900 also shows a low Tafel slope of 47.3 mV dec À 1 , which is much lower than those of GTCo800 (109.4 mV dec À 1 ) and GTCo1000 (59.1 mV dec À 1 ). According to the above results, the high current density and low Tafel slope indicate that GTCo900 possesses the best HER kinetics, among the as-prepared electrocatalysts.…”

“…To tackle these issues, non‐noble metal contained materials have received considerable researches . Among all of the catalysts, numerous efforts have been focused on Co 9 S 8 ‐based composites, which are proved to reveal superior electrocatalytic performance for HER …”

“…[14,15] Among all of the catalysts, numerous efforts have been focused on Co 9 S 8 -based composites, which are proved to reveal superior electrocatalytic performance for HER. [16][17][18][19][20][21][22][23] Mesoporous carbons have received considerable research efforts, owning to tunable pore sizes, high surface areas, and outstanding electrical conductivity. [24][25][26][27][28][29][30] However, when using as catalysts for the electrocatalysis, such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR), mesoporous carbons can barely reveal superior electrocatalytic activity, owning to chemical inertness.…”

Surface and Interface Engineering: Molybdenum Carbide–Based Nanomaterials for Electrochemical Energy Conversion

“…Considering these advantages of MOFs as discussed above, MOF-assisted strategy has been employed to construct molybdenum carbide-based catalysts for OER and overall water splitting. [129,204,222,223] For example, Luo et al prepared a heterostructure composed of cobalt sulfide (Co 9 S 8 ) and molybdenum carbide (Mo 2 C) nanoparticles anchored on porous N, S-codoped graphitic carbon (Co 9 S 8 -NSC@Mo 2 C) as a bifunctional electrocatalyst through a simple MOF-assisted pyrolysis method (Figure 14a). [223] The as-prepared Co 9 S 8 -NSC@Mo 2 C sample showed a typical dodecahedron shape with rough surface due to the carbonization process as shown in Figure 14b.…”