Facile Synthesis and Electrocatalytic Activity of Sulfur Doped Carbon for Oxygen Reduction
Authors: Yang Ruizhi , Sun Yan , Yang Zhenrong , Wu Jiao 
Published: February 2020

Fuel cells and metal-air batteries have attracted much attention over the past few years due to their high energy density and the potential to reduce the negative impact of climate change [1,2]. However, the sluggish oxygen reduction reaction (ORR) at the cathode, which requires highly efficient and low cost electrocatalysts, is one of the important factors that restrict the wide application of fuel cells [3-5]. Exploring low-cost and sustainable electrocatalysts with high efficiency to alternate the platinum-based noble electrocatalysts for the ORR is critical for the development of fuel cells and metal-air batteries [6-8].
Heteroatom-doped carbon materials have emerged as promising alternative electrocatalyts for the ORR due to its low price, high catalytic activity and environmental friendliness [6-13]. The heteroatom doped in carbon is usually N, S, B, F and P et al., which can modify the electronic structure (like charge and/or spin density redistribution) of carbon and create the active sites favorable for the adsorption of O2 molecule and facilitate the ORR process [9-13]. Considerable efforts have been devoted to the study of N-doped carbon catalysts for the ORR[14-17]. Sulfur doping is also convinced to be a valid method in promoting the catalytic activity of carbon towards ORR. Sulfur has an electronegativity of 2.58, which is similar to carbon’s (2.55) [12]. In contrast, the electronegativity of N(3.04) is higher than that of carbon. Therefore the modification of structure and the catalytic activity of carbon resulting from N doping and S doping is different. S-doped graphene has been reported to show improved electrocatalytic activity for ORR [11,18]. Nevertheless, there have been few reports about the ORR activity of S-doped porous carbon. It’s known that porous carbon can provide effective triple phase (solid-liquid-gas) region for the mass transfer of reactants and products during the ORR.
To better understand the effect of S-doping on the structure and ORR activity of carbon, we developed a facile method to synthesize the S-doped porous carbon via a hydrothermal method with sucrose and benzyl disulfide (BDS) as the carbon and sulfur sources, respectively. The influence of S doping on the electrocatalytic activity of the carbon for the ORR in alkaline media was investigated. The pyrolysis temperature has a significant impact on the structure and texture of the S-doped carbon, which further affects the ORR activity and durability of S-doped carbon as shown in Figure 1.

Acknowledgements

This work is supported by National Natural Science Foundation of China (Nos.51272167 and 21206101 ).

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Figure 1. Linear sweeping voltammograms of the ORR on the S-doped carbon samples in 0.1 M NaOH solution with a rotating speed of 1600 rpm.

Figure 1