Synthesis of Nano-Porous Ti/TiO2/Ni-W-B Electrode for Electrocatalytic Reduction of Coal

1      Introduction

Electrochemical hydrogenation of coal is a novel method for coal liquefaction, which applies electrical energy instead of high temperature and pressure to liquefy coal in direct coal liquefaction. However, the electrochemical coal reduction is limited by the sluggish cathode reaction kinetics.

Nano-porous TiO₂ has been received increasing attention due to its unique properties, such as large surface-to-volume ratio, uniform pore diameter and quantum size effect. Therefore, nano-porous TiO₂ exhibited special performance in optics, chemistry and other fields with huge advantage compared with normal nano-TiO₂ [1].

Amorphous alloy catalyst with a unique short-range ordering but long-range disordering structure, and a high concentration of coordinately unsaturated sites, has been widely applied in hydrogenations [2]. In comparison with other binary Ni-based catalysts, the Ni-B amorphous catalysts exhibited high activity and selectivity, showing the promoting effect from alloying B on the hydrogenating reactions. Addition of a second metal such as W to Ni-B amorphous alloy catalyst could greatly enhance the activity in hydrogenation [3].

In this report, we mainly focused the catalytic effects of nano-porous Ti/TiO₂/ Ni-W-B electrode as a cathode for coal electroreduction.

2     Experimental

2.1 Preparation of nano-porous Ti/TiO₂/Ni-W-B electrode

Anodization coupled with electrodeposition was employed to prepare the nano-porous Ti/TiO₂/Ni-W-B electrode, which used as the cathode for coal electroreduction.

2.2 Characterization of prepared electrodes

The prepared electrodes were characterized by scanning electron microscopy (Hitachi SEM 6700F), X-ray diffraction analysis (XRD-2700, Dandong). Electrochemical measurements were carried out with a CHI660B electrochemistry workstation (CHI, China).

2.3 Electrolysis and Extraction of product

The electrolysis cell was divided into two parts including anode and cathode by a microporous membrane. The cathode electrolyte volume was 40 mL, which consisted of 0.5 mol/L TBAB, 2.5 mol/L H₂O, 20 g/L coal and DMF-EtOH (vol) = 2:3. The composition and volume of anode electrolyte were the same as the cathode solution but without coal. Extraction yield was calculated from the quality of THF soluble components dividing the quality of coal particles (0.8 g).

3      Results and discussion

Figure 1 shows the SEM micrograph of the nano-porous TiO₂film, which is prepared by anodization experiment, is a multiple porous network structure. The average size of the pore diameter is about 200 nm. After electrodeposition of Ni-W-B alloy catalyst, the surface of nano-porous TiO₂ film was mostly covered by smaller size Ni-W-B particles which were shown in Fig. 1B.

Figure 2 shows the LSV behavior of the electrodes in above organic system with coal at a sweep rate of 50 mV/s. The electrodeposition of catalyst increased the performance of electrodes significantly, demonstrating the positive effect of Ni-W-B amorphous alloy catalyst for coal reduction. It is also noticed that the improved performance of the nano-porous electrodes is obvious, illustrating the favorable nano-porous structure to the improvement of the coal electroreduction.

Table 1 shows the liquid extraction yields of the coal electroreduction with different electrodes. The extraction yields increased with the different electrodes and obtained the maximum yield (34.5%) with the nano-porous Ti/TiO₂/Ni-W-B electrode.

4      Conclusions

The prepared nano-porous Ti/TiO₂/Ni-W-B electrode with multiply nano-porous structure improved the coal electroreduction current obviously and increased the extraction yield of THF soluble components effectively, promising to be a great application prospect for electrocatalytic reduction of coal and other probable electroreductions.

Acknowledgements

We gratefully acknowledge the National Science Foundation of China (No. 20673071, 20873083 and 21173144), and the State Key Laboratory of Chemical Engineering (No. SKL-ChE-08A01).

References

[1] X.B. Chen, S.S. Mao,Chem. Rev. 107 (2007) 2891.

[2] W.Y. Wang, Y.Q. Yang, H.A. Luo, H.Z. Peng, B. He, W.Y. Liu, Catal. Commun. 12 (2011) 1275.

[3] L.F. Chen, Y.W. Chen,   Ind. Eng. Chem. Res. 45 (2006) 8866.