2D Monoelements. Группа авторов
the best-performing control and SANs devices measured at different scan rates. (d) EQE spectra at maximum power output point for best-performing control and SANs devices. (a, b) Reproduced with permission [21]. Copyright 2018, Wiley-VCH. (c, d) Reproduced with permission [48]. Copyright 2018, Wiley-VCH.
2.4.3 Electrocatalysis
Two-dimensional materials with atomic-scale thickness have more active sites and defects, as well as larger surface areas, which can achieve much higher catalytic activity than their bulk counterpart. Therefore, these 2D electrocatalysts can be effectively used to catalyze the CO2 reduction reaction (CO2RR), HER, and oxygen evolution reaction (OER) [51–53]. Combining the advantages of metals and non-metals, 2D semi-metals with high carrier concentration and short charge transfer channel exhibit enhanced catalytic activity for low catalytic threshold and efficient charge transfer [54]. Few-layer antimonene is expected to be employed as an active 2D electrocatalyst due to its semi-metallic nature.
Li et al. produced few-layer antimonene nanosheets (SbNSs) by cathodic exfoliation, then applied them into the electrocatalytic process of CO2RR [55]. Compared with bulk Sb, few-layer SbNSs exposed more active edge sites, thus could obtain higher catalytic efficiency. Figure 2.9a shows the linear-sweep voltammetric (LSV) curves of bulk Sb- and SbNSs-modified working electrodes recorded in N2- and CO2-saturated 0.5 M NaHCO3 solutions, it is observed that the SbNSs electrode exhibits a lower onset potential and a significantly enhanced catalytic current density compared to bulk Sb electrode. At the same time, the SbNSs electrode shows a broad peak with the center position at −1.06 V in the CO2-saturated NaHCO3 solutions. The reduction products are composed of H2, CO, and formate. Furthermore, they also prepared few-layer antimonene nanosheet-graphene (SbNS-G) composites, then compared their catalytic activity with SbNSs, concluding that SbNS-G-modified electrode possessed a higher Imass than SbNSs electrode. As illustrated in Figure 2.9b, the SbNS-G also presented an enhanced selectivity towards product formate at lower overpotentials, where the maximum faradaic efficiency (FE) was 88.5% at an overpotential of 0.87 V (potential of −0.96 V) higher than 84% of SbNSs (potential of −1.06 V). Moreover, the partial current density for formate of SbNS-G at −1.07 V is 1.5 and 16 times larger than that of SbNSs and bulk Sb, respectively (Figure 2.9c). The enhanced catalytic performance of SbNS-G is attributed to the strong electronic interaction between SbNS and graphene.
Figure 2.9 (a) LSV curves of bulk Sb- and SbNSs-modified glassy carbon electrodes in N2- and CO2-saturated 0.5 M NaHCO3 solutions. Scan rate is 50 mVs−1. FE (b) and partial current density (c) for formate of bulk Sb, SbNSs, and SbNS-G. Polarization curves and Tafel plots of antimonene nanosheets for HER (d) and OER (e) in KOH solutions with different concentrations (0.1, 0.2, 0.5, and 1 M). (f) Long-term stability of antimonene nanosheets in 0.5 M KOH. The bias potentials for HER and OER are −1.6 and 1.2 V, respectively. (a–c) Reproduced with permission [55]. Copyright 2017, Wiley-VCH. (d–f) Reproduced with permission [54]. Copyright 2019, American Chemical Society.
After that, Ren et al. adopted LPE-produced few-layer antimonene nanosheet as a metal-free electrocatalyst for full water splitting in alkaline condition [54]. The antimonene nanosheets showed great potentials in catalyzing both HER and OER, because of the semi-metallic nature together with increased active sites and larger surface area compared to bulk Sb. The lowest Tafel slope of antimonene nanosheets was 217.2 mV dec−1 for HER in 0.5 M KOH and 261.3 mV dec−1 for OER in 1 M KOH (Figures 2.9d, e). Additionally, bifunctional antimonene nanosheets presented a long-term stability in KOH solution, benefiting for durable and efficient electrocatalysis of full water splitting (Figure 2.9f).
2.4.4 Energy Storage
On the strength of high theoretical capacity of 660 mAh g−1, increased active sites, and fast ion diffusion, few-layer antimonene is considered to be a promising electrode material in the energy storage applications, such as sodium-ion batteries (SIBs), lithium-ion batteries (LIBs), and supercapacitors [56–59].
Gu et al. obtained free-standing metallic Sb nanosheets via the LPE method, then fabricated SbNS-G hybrid films with tunable densities, which were subsequently applied to the SIBs [56]. The volumetric capacity of SbNS-G film (1.6 mg cm−2) reached to 1,226 mAh cm−3 in the initial cycle (Figure 2.10a), which was higher than the value of previously reported Sb/C nanocomposites (100–300 mAh cm−3) and graphene film (80 mAh cm−3). Furthermore, SbNS-G film also exhibited a high-rate capacity with both charge and discharge volumetric capacity of 216 mAh cm−3 at a current density of 4.0 mA cm−2 (Figure 2.10b), this result was superior to that of graphene film (13 mAh cm−3). SbNS-G film showed simultaneously a good cycle performance for sodium (Na) storage, where the capacity was still stabilized at 110 mAh cm−3 after 100 cycles at high current density (4.0 mA cm−2). Afterwards, Tian et al. studied the Na storage performance and mechanism of 2D FLA from experiments to theoretical calculations [57]. The FLA electrode delivered a charging capacity of 642 mAh g−1 at a current density of 0.1 C and a rate capacity of 429 mAh g−1 at 5 C, as well as a stable capacity of 620 mAh g−1 at 0.5 C after long-term charging/discharging cycles, which meant the utilization ratio of Sb atoms was as high as 93.9 % (Figures 2.10c, d). For the Na storage mechanism, they thought that FLA experienced a sodiation/desodiation process, where Na first reacted with Sb to form crystalline NaSb intermediate phase then to crystalline Na3Sb in the sodiation process, conversely during the desodiation process, Na3Sb first transformed to NaSb then to Sb with a small number of NaSb. This reversible crystalline-phase evolution was also accompanied by anisotropic volume expansion to achieve structural stability and electrochemical redox kinetics. In addition, FLA also exhibited high-rate lithium (Li) storage capabilities, even without the help of additives [58]. As shown in Figure 2.10e, the stable capacity of FLA after 100 cycles at 0.5 C was 584.1 mAh g−1 with CE of ~100%, which was higher than that of Sb nanoparticles (NPs) (552.3 mAh g−1). FLA displayed a rate capacity of 488 mAh g−1 at 5 C, corresponding to 74% capacity retention of the value at 0.1 C, while the rate capacity of Sb NPs was 443 mAh g−1 at 5 C, and this value was only 67% of the initial capacity at 0.1 C (Figure 2.10f). The higher rate performance of FLA than Sb NPs was attributed to the preferential Li ion dispersion along in-plane channel in FLA.