Photocatalytic hydrogen generation
over semiconductor photocatalysts
has attracted considerable attention over the past few decades. This
experiment is designed for sophomore- and higher-level undergraduates
who are in the majors of materials chemistry, analytical chemistry,
catalysis, or chemical engineering. In this experiment, CdS nanoparticles
and nanosheets were first fabricated with a one-step direct-precipitation
reaction and a two-step precipitation–ion-exchange reaction,
respectively, and then used as photocatalysts for visible-light
hydrogen evolution from water, in the presence of noble-metal Pt nanoparticles
as in situ cocatalysts and sodium sulfide and sulfite (Na2S/Na2SO3) as sacrificial reagents. A gas chromatograph
with a thermal-conductivity detector (GC-TCD) was used to quantitatively
monitor the produced hydrogen gas. This interdisciplinary experiment
is expected to give students an introduction to nanomaterial synthesis,
the general process of photocatalytic hydrogen generation, and the
principles and use of instruments. Upon the completion of the experiment,
students understand how chemistry can be utilized for renewable-energy
applications.
Flexible rechargeable Zn//Ni batteries are attractive owing to their high energy density, good safety, inexpensive cost, and simple manufacturing process. However, the effects of metal doping on the properties of Ni 3 S 2 cathodes in Zn/Ni batteries are not well understood. Herein, a binder-free Ni 3 S 2 electrode is doped with Zn and Co and the nanocomposite structures are prepared on nickel foam (named ZCNS/NF) by a simple two-step hydrothermal technique. The ZCNS/NF//Zn battery delivers excellent electrochemical performance such as a working voltage window can be as high as 2.05 V, a capacity of 2.3 mAh cm −2 at 12 mA cm −2 , and 82% retention going through 2000 cycles at 20 mA cm −2 . The battery has a maximum output area energy density of 1.8 mWh cm −2 (462 Wh kg −1 ) and a power density of 36.8 mW cm −2 (9.2 kW kg −1 ). In addition, the flexible battery remains operational while being bent at a large angle and even punctured. The high performance and robustness of the composite cathode suggest that the design principle and materials have large commercial potential in Ni//Zn batteries.
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