A temperature-dependent phosphorus doping on Ti3C2Tx MXene for enhanced supercapacitance

Microwave-assisted rapid synthesis of titanium phosphate free phosphorus doped Ti3C2 MXene with boosted pseudocapacitance

“…On further deviation from the given conditions, the P doping level drops down to 1.28 wt% (0.91 at%, as calculated from XPS), which may ultimately reduce the electrochemical storage performance of the same. In contrast, optimization during conventional heating presented in Table S1 † indicates the dominance of various phosphate formation under almost every given condition (among the formed phosphate phases, titanium phosphate is common but sodium phosphate has also been formed in the case of the SDP doping source as further discussed in the XRD section), which is in line with a recent report, 35 where P doping in Ti 3 C 2 T x is also carried out through a conventional heating process in the presence of sodium hypophosphite as the doping source. We believe that not only the heating method but the choice of doping source and mixing quality of the reaction precursors have also played a major role in the development of titanium phosphate free P-Ti 3 C 2 with maximum doping.…”

“…However; conventional heating is a slow process, where heat travels from the surface to the core and provides enough time to alter the Ti 3 C 2 T x phase structure to produce P-Ti 3 C 2 -An like TiP 2 O 7 , TiPO 4 , Ti(PO 3 ) 3 , Ti 3 (PO 4 ) 4 and many others. As mentioned in the Introduction section, 35,36 in the presence of oxygenated functional groups and a longer reaction time, Ti-based materials are highly prone to form titanium phosphates through a phase change reaction and it might be the case with the conventional heating of Ti 3 C 2 T x in the presence of P doping sources as well. So, the choice of doping source, homogeneity of the mixture, and selection of a suitable heating method are extremely important to develop titanium phosphate free P-Ti 3 C 2 with adequate P doping to boost the electrochemical storage performance of Ti 3 C 2 T x .…”

“…Peak shiing and broadening in layered nanoscale materials including MXenes are very common during doping because the insertion of dopants (in the present case, it is the P dopant) into the MXene lattice creates inhomogeneous localized structural distortions and strains. 28,34,35,50,51 For example, an earlier report on P doping in Ti 3 C 2 T x has also experienced peak shiing and broadening aer doping, because it creates distortion in MXene layers. 35 Likewise, during N doping in Ti 3 C 2 T x also peak broadening along with shiing is observed.…”

“…have indicated that undesired titanium phosphate forms during doping, which needs to be removed to achieve its said performance. From previous studies [34][35][36][37] also it is evidenced that long thermal exposure of Ti based systems in the presence of oxygenated functional groups and P sources leads to the formation of titanium phosphates through a phase change reaction. Though a few metallic phosphates are known to be potential candidates to generate pseudocapacitance and enhance the overall performance of energy storage devices, they are highly structure dependent.…”

“…26 Subsequently, the large P atom having a high electrondonating tendency has also been tried in Ti 3 C 2 T x doping via the conventional heating method and applied for supercapacitor applications. 35 The developed P-Ti 3 C 2 based supercapacitor electrode has produced a gravimetric capacitance of 320 F g À1 at a low current density of 0.5 A g À1 and in a narrow potential window of 0.6 V in a 1 M H 2 SO 4 electrolyte. This same P-Ti 3 C 2 electrode shows an energy density of 8.07 W h kg À1 and power density of 52.8 W kg À1 with a capacitance retention of 83.8% aer 5000 cycles, which is surely not amongst the highest and not suitable for various practical applications.…”