Co₉S₈@N,P-doped porous carbon electrocatalyst using biomass-derived carbon nanodots as a precursor for overall water splitting in alkaline media

Abstract

In this study, we first synthesized Co 9 S 8 @N-doped porous carbon (Co 9 S 8 @NC) using shrimp-shell derived carbon nanodots as a carbon/nitrogen source in the presence of CoSO 4 by a one-step molten-salt calcination method. This was followed by low-temperature phosphorization in the presence of NaH 2 PO 2 , whereby Co 9 S 8 @N,P-doped porous carbon (Co 9 S 8 @NPC) was finally obtained using the Co 9 S 8 @NC as a precursor. The results demonstrated that the molten-salt calcination approach can effectively create a pyrolytic product with a porous structure and improve the material's surface area, which is favourable for electrocatalysis-related mass transport and the exposure of catalytic active sites during electrocatalysis. As an electrocatalyst, Co 9 S 8 @NPC exhibits higher catalytic activity for the hydrogen evolution reaction (HER) than Co 9 S 8 @NC in an alkaline medium. Among all the investigated Co 9 S 8 @NPC catalysts, Co 9 S 8 @NPC-10 (mass ratio of NaH 2 PO 2 to Co 9 S 8 @NC ¼ 10 : 1) displays the best HER activity with an overpotential of 261 mV at 10 mA cm À2 in the alkaline medium. Interestingly, Co 9 S 8 @NPC-10 also displays good catalytic activity for the oxygen evolution reaction (OER) in this study.Owing to its bifunctional catalytic activity towards the HER and OER, the fabricated Co 9 S 8 @NPC-10 was simultaneously used as an anode and cathode material to generate O 2 and H 2 from overall water splitting in the alkaline medium, exhibiting a nearly 100% faradaic yield. This study would be helpful to the design and development of high performance non-precious metal electrocatalysts to be applied in overall water splitting to produce H 2 and O 2 . IntroductionElectrocatalytic water splitting has been widely regarded as a potential renewable and sustainable energy technology to generate H 2 for replacing traditional fossil fuels, and H 2 has a high energy density and an environmentally-friendly combustion product. 1-3 To drive electrocatalytic water splitting to generate H 2 , an active electrocatalyst for the hydrogen evolution reaction (HER) is critically important, which would reduce the overpotential for the HER, thereby making the whole water splitting process more energy efficient. To date, the most efficient HER electrocatalysts are almost exclusively applied in acidic media owing to the rapid reaction rate of H + to H 2 on the catalyst surface, 4-8 however, studies on HER catalysts in alkaline media are relatively rare due to the more complex reaction mechanism of OH À on the catalyst surface and the sluggish kinetics of the counterpart electrode reaction for the oxygen evolution reaction (OER) during electrocatalytic water splitting. 9-11 So far, Pt-based and Ru/Ir-based catalysts have been extensively considered as the most active electrocatalysts for the HER and OER respectively in alkaline media, however, their high costs and source scarcity have limited large-scale production applications.3,7,12-14 Therefore, searching for cheap, earthabundant and efficient electrocatalysts with hi...

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

“…In comparison to bulk Co 9 S 8 , nanostructured Co 9 S 8 and its composites could afford more active sites and faster transfer rate of ions/electrons during the electrocatalytic reaction, and thus usually exhibiting enhanced HER and OER activities. [20][21][22][23][24] Currently, several Co 9 S 8 nanostructures (e.g., nanoparticles [25] and nanospheres [26] ) and their composites with carbons (Co 9 S 8 /reduced graphene oxides (RGO), [22] Co 9 S 8 /(N, S, P)-doped carbons, [27] Co 9 S 8 /Fe 3 O 4 / RGO, [23] and Co 9 S 8 /MoS 2 /Carbon fibres [25] ) have been reported. For example, Co 9 S 8 /N,P-carbon powder nanocomposites prepared by molten-salt calcination method at 900 °C exhibited an HER overpotential of 261 mV at 10 mA cm −2 in alkaline medium.…”

“…For example, Co 9 S 8 /N,P-carbon powder nanocomposites prepared by molten-salt calcination method at 900 °C exhibited an HER overpotential of 261 mV at 10 mA cm −2 in alkaline medium. [20] N-Co 9 S 8 /graphene nanocomposites was achieved Designing ever more efficient and cost-effective bifunctional electrocatalysts for oxygen/hydrogen evolution reactions (OER/HER) is greatly vital and challenging. Here, a new type of binder-free hollow TiO 2 @Co 9 S 8 core-branch arrays is developed as highly active OER and HER electrocatalysts for stable overall water splitting.…”

Fabrication of a 3D Hierarchical Sandwich Co9S8/α‐MnS@N–C@MoS2 Nanowire Architectures as Advanced Electrode Material for High Performance Hybrid Supercapacitors

“…The high‐resolution C 1s spectrum (Figure d) can be deconvoluted into four peaks at 284.6, 285.2, 286.1, and 290.0 eV, which correspond to CC/CC, CN, CO, and CO, respectively . The high resolution N 1s spectrum (Figure e) can be deconvoluted into four peaks, which are correlated to various electronic states of nitrogen functional groups, such as pyridinic N (398.7 eV), pyrrolic N (399.9 eV), graphitic N (401.2 eV), and quaternary N (402.4 eV), indicating successful doping of nitrogen into the carbon matrix . This is due to the fact that the nitrogen doping can improve the electrical conductivity of the carbon matrix, which results in improved electrochemical performance.…”

Assembling Co9S8 nanoflakes on Co3O4 nanowires as advanced core/shell electrocatalysts for oxygen evolution reaction

“…Of these candidates, cobalt sulfide (Co 9 S 8 ) has been the subject of intense research because of its high catalytic activity and superior electrochemical stability for OER [18,19] . Though cobalt sulfide is endowed with these fascinating virtues, the OER performance of the bulk Co 9 S 8 is still unsatisfactory due to poor electronic conductivity and little exposed active sites [20][21][22] .…”

“…Up to now, a variety of Co 9 S 8 electrodes have been reported by developing Co 9 S 8 nanostructures or compositing with conductive matrixes. For instance, Co 9 S 8 @N/P-doped carbon composite electrocatalysts prepared by Liu et al [18] exhibited a low overpotential of 400 mV at 10 mA cm −2 by a one-step molten-salt calcination method. Cao et al [23] reported cobalt sulfide/porous N-doped carbon with a low Tafel slope of 65 mV dec −1 by a high-temperature calcination method.…”