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The charge-storage kinetics of amorphous TiO x nanotube electrodes formed by anodizing three-dimensional porous Ti scaffolds are reported. The resultant electrodes demonstrated not only superior storage capacities and rate capability to anatase TiO x nanotube electrodes but also improved areal capacities (324 μAh cm–2 at 50 μA cm–2 and 182 μAh cm–2 at 5 mA cm–2) and cycling stability (over 2000 cycles) over previously reported TiO x nanotube electrodes using planar current collectors. Amorphous TiO x exhibits very different electrochemical storage behavior from its anatase counterpart as the majority of its storage capacity can be attributed to capacitive-like processes with more than 74 and 95% relative contributions being attained at 0.05 and 1 mV s–1, respectively. The kinetic analysis revealed that the insertion/extraction process of Li+ in amorphous TiO x is significantly faster than in anatase structure and controlled by both solid-state diffusion and interfacial charge-transfer kinetics. It is concluded that the large capacitive contribution in amorphous TiO x originates from its highly defective and loosely packed structure and lack of long-range ordering, which facilitate not only a significantly faster Li+ diffusion process (diffusion coefficients of 2 × 10–14 to 3 × 10–13 cm2 s–1) but also more facile interfacial charge-transfer kinetics than anatase TiO x .

Although Si anodes have the potential to achieve gravimetric capacities >3000 mA g −1 for Li ion batteries, their utility has been limited by their large volumetric expansion on lithiation and electrode fragmentation. We show that n-type doping reduces the lithiation potential of (100) Si and conclude that the Li ion insertion energy into crystalline Si increases with ntype dopant density. This allows tuning of the n-type dopant density in Si electrodes to reduce surface fragmentation and increase electrode cycle life. Using a combination of n-type doping, prelithiation at a low current density of 0.05 mA cm −2 and an areal capacity capping at 2 mAh cm −2 , we show that stable cycling can be achieved at a current density of 1 mA cm −2 within the potential range of 0.01−1.5 V for at least 140 cycles using an organic electrolyte without additives. Further improvements in cyclability can be achieved by using alternative electrolytes with greater electrochemical stability at low potentials. Because of the massively reduced cost of Si wafers, heavily doped wafer-based current collectors may present an alternative to Si thin film anodes with improved adhesion between the current collector and electroactive Si surface provided that the wafers can be sufficiently thin to reduce electrode mass and volume. Alternatively, n-type doping of Si can be used to reduce fragmentation in particle-based electrodes permitting more controllable lithiation and a longer cycle life.

demonstrated performance in the field for at least 25 years. This suggests that hybrid devices based on c-Si PV technology have a more promising pathway into utility-scale electrical grids. Westover et al. reported a c-Si based hybrid device in which a porous Si electric double-layer capacitor (EDLC) was integrated on the rear surface of a c-Si solar cell after removal of the screen-printed aluminum (Al) rear electrode. [11] However, the large surface area required for charge storage in the porous silicon EDLC inevitably increased the surface recombination, and significantly reduced the open-circuit voltage (V OC ) and therefore the efficiency of the solar cell. [3] In another hybrid device employing the c-Si solar cell, a laser scribed graphene oxide (LSGO) supercapacitor was fabricated on the back of the solar cell. [12] By using an insulation layer between the supercapacitor and the solar cell, the solar cell performance was not degraded. However, this was at the cost of relatively high complexity, as the electrodes of the solar cell and the capacitor were independent. Furthermore, the capacitance may be limited by the thickness of the LSGO electrode and the need to support both electrodes on the rear surface of the solar cell.Both high power and energy densities are desirable for storing PV energy. Fast charge and discharge rates are necessary to quickly respond to the ever-changing sunlight conditions, and effective buffering of PV power requires at least a few minutes of high power discharge when the sunlight is insufficient to meet demand. [4,8] Pseudocapacitive transition metal oxides typically have significantly higher power densities, quicker response times and longer cycle lives than batteries; compared with EDLCs, they have higher energy density due to Faradaic reactions complementing that of double layer electrostatic adsorption. [13,14] For the nanostructured molybdenum oxide (MoO x ) in particular, multiple charge storage mechanisms has been demonstrated, including ion insertion, surface redox pseudocapacitance, and EDL capacitance, [14,15] making it an ideal pseudocapacitive material with high power and energy delivery for PV applications.In this Communication, we report a novel hybrid energy harvesting-storage architecture consisting of an anodic amorphous MoO x (a-MoO x ) pseudocapacitive electrode monolithically integrated on the rear Al electrode of an industrial screen-printed Si solar cell, as shown in Figure 1a. The solar cell and the pseudocapacitor share a common electrode. Compared with previous studies, [11,12] this design has the advantages of integration simplicity and minimum resistive loss of the threeterminal architecture, and avoids degrading the performance of the solar cell. Details of the device fabrication process can The global photovoltaic (PV) power generation in 2015 exceeded 200 GW. [1] Accounting for more than 15% of net supply additions, PV electricity generation is the second-fastest growing source in the world's power sector. [2] However, the direct dependence of PV g...