Effect of Synthesis Parameters on the Electrochemical Properties of High‐Surface‐Area Mesoporous Titanium Oxide with Polypyrrole Nanowires in the Pores

Abstract

This paper describes the synthesis and characterisation of high‐surface‐area mesoporous titanium oxides with polypyrrole nanowires within the pores, and the subsequent variation of synthesis parameters such as polymer‐loading level and pore size to improve performance. These modifications are employed to improve the electron conductivity of the amorphous host and exploit the high internal surface areas of over 800 m2g−1 for potential use as a lithium battery cathode material, once fully optimised, with fast charge‐transfer kinetics expected from the proximity of the vast majority of the redox sites at, or near, the surface of the inner pore walls. A full structural characterisation, in addition to electrochemical assessments, of the composite materials is presented and compared to the pristine mesoporous titanium oxide hosts. The best synthesis conditions were achieved with 5 % polymer loading and the largest pore sized host materials. Excessive polymer loading and smaller pore sizes lead to decreased performance, possibly due to inhibition of Li+ transport. The C18 templated TiO2 composite produced the best capacity retention at 58 % retention, and the C12 composite produced the highest initial capacity of 170 mAh g−1 by using a current density of 1 mAcm−2.

Low‐Temperature Synthesis and Electrochemical Properties of Mesoporous Titanium Oxysulfides

“…For all materials synthesized at 150 °C, there is a broad reflection at approximately 2 θ =1–2°. This reflection at similar intensity is also observed in pristine m ‐TiO 2 and is diagnostic of a wormhole pore structure, as demonstrated in previous work . The patterns for materials synthesized with different heating temperatures (Figure S3) also display this reflection; however, there is a slight decrease in the reflection intensity relative to the pristine sample, indicating some degree of structure loss.…”

“…The nitrogen adsorption isotherms for samples synthesized at 100, 150, and 200 °C with 3.5 mL of HMDST can be seen in Figure S1. The isotherm of the material synthesized at the lowest temperature of 100 °C falls between type 1 and type 4, suggesting the retention of pore structure with only small‐to‐moderate loss of surface area, whereas the samples synthesized at 150 and 200 °C possess isotherms that resemble more closely type 2 isotherms, suggestive of a substantial loss of surface area, owing to pore blockage or collapse . Following this predicted trend, the BET surface areas of the composite materials drop from 660 to 66 and 41 m 2 g −1 upon an increase of the synthesis temperature from 100 to 150 and 200 °C, respectively, at a loading level of 3.5 mL.…”

“…Mesoporous transition‐metal oxides typically show an initial endothermic weight loss up to 200 °C, caused by the loss of residual solvents present within the sample. After a temperature of 250 °C is reached, all materials show a sharp increase towards positive values in the DTA plot, typically indicating the start of the exothermic process in these samples . The weight loss between 0 and 250 °C can be used to determine the desorption of residual solvent within the samples.…”

“…Further work using pyrrole to investigate the effects of doping levels and pore sizes yielded materials fully optimized for this approach. By using a low polymer loading with larger pore sizes, improvements in conductivity and Li transport were achieved with minimum weight gain . However, cycling performance was still insufficient relative to competitive battery materials.…”

“…By using al ow polymer loading with larger pore sizes, improvements in conductivity and Li transport were achievedw ith minimum weight gain. [19] However,c ycling performance was still insufficient relative to competitive battery materials. Most recentlyi no ur group, similar methodologies were employed by using photopolymerization in place of ac hemical oxidanti nt he hope that improving the interface between the host and threaded polymer nanowires would further improve the conductivity and capacity; [20] however,s imilar results were observed, with polymer loadings of 5% being optimal.…”