Transition metal oxides hold great promise for lithium‐ion batteries (LIBs) and electrocatalytic water splitting because of their high abundance and high energy density. However, designing and fabrication of efficient, stable, high power density electrode materials are challenging. Herein, we report rambutan‐like hollow carbon spheres formed by carbon nanosheet decorated with nickel oxide (NiO) rich in metal vacancies (denoted as h‐NiO/C) as a bifunctional electrode material for LIBs and electrocatalytic oxygen evolution reaction (OER). When being used as the anode of LIBs, the h‐NiO/C electrode shows a large initial capacity of 885 mA h g−1, a robust stability with a high capacity of 817 mA h g−1 after 400 cycles, and great rate capability with a high reversible capacity of 523 mA h g−1 at 10 A g−1 after 600 cycles. Moreover, working as an OER electrocatalyst, the h‐NiO/C electrode shows a small overpotential of 260 mV at 10 mA cm−2, a Tafel slope of 37.6 mV dec−1 along with good stability. Our work offers a cost‐effective method for the fabrication of efficient electrode for LIBs and OER.
The ability to achieve dual-mode thermal regulation for switchable heating and cooling on a single platform has thus far been challenged by the availability of suitable materials. The materials need to possess both high solar reflectance and high transmittance, necessitating large and small thicknesses in the same coating layer, respectively (i.e., the thickness constraint). Herein, for the first time, a single-layer coating made in a facile one-step process is reported, which exhibits rapid switch between high solar reflection (≈96.6%) and high solar transmission (≈86.6%). In the dry state, high solar reflectance and infrared (IR) emittance (>96% from 8 to 13 µm) enable passive radiative cooling, resulting in all-day near/sub-ambient temperatures in the demanding weather conditions of the tropical climate. Upon wetting, high transparency in the broadband range (0.3-2.5 µm) allows solar heating, leading to switchable thermal regulation. Such unprecedented performances are achieved through a unique hierarchical porous structure comprising of vertically aligned microscale pores in nanoscale pore matrix. This structure breaks the thickness constraint and broadens its applicability, in particular for seasonal areas with large temperature variation throughout the day.
Alkaline water electrolysis (AWE) holds great promise for a truly sustainable energy future if it can be driven by renewable energy sources such as solar and wind. The main challenge arises from the serious partial loading issue when intermittent and unstable renewable energy is coupled to water electrolyzers. An energy storage device can mitigate this incompatibility between water electrolyzer and renewable energy sources. Herein, an AWE device driven by solar photovoltaic (PV) through a full cell of lithium‐ion battery (LIB) as an energy reservoir is demonstrated (PV−LIB−AWE). Stable power output from LIB drives the water electrolyzer for steady hydrogen production, and thus overcomes the partial loading issue of AWE. Moreover, a multifunctional hierarchical material, porous nickel oxide decorated nitrogen‐doped carbon (NC) support, with excellent electrochemical performances for LIBs, oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) for the PV−LIB−AWE system is developed. Density functional theory calculations show that the strong interaction between metal oxide and NC tailors the electronic structure and then optimizes activation energy of OER process. PV−LIB−AWE integrated system demonstrated here offers an alternative approach to drive water electrolysis with intermittent renewable energy for a truly sustainable energy future.
The creation of pseudo-magnetic fields in strained graphene has emerged as a promising route to investigate intriguing physical phenomena that would be unattainable with laboratory superconducting magnets. The giant pseudo-magnetic fields observed in highly deformed graphene can substantially alter the optical properties of graphene beyond a level that can be feasible with an external magnetic field, but the experimental signatures of the influence of such pseudo-magnetic fields have yet to be unveiled. Here, using time-resolved infrared pump-probe spectroscopy, we provide unambiguous evidence for slow carrier dynamics enabled by the pseudo-magnetic fields in periodically strained graphene. Strong pseudo-magnetic fields of ~100 T created by non-uniform strain in graphene on nanopillars are found to significantly decelerate the relaxation processes of hot carriers by more than an order of magnitude. Our findings offer alternative opportunities to harness the properties of graphene enabled by pseudo-magnetic fields for optoelectronics and condensed matter physics.
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