The development of
bifunctional electrocatalysts with high performance
for both hydrogen evolution reaction (HER) and oxygen evolution reaction
(OER) with earth-abundant elements is still a challenge in electrochemical
water splitting technology. Herein, we fabricated a free-standing
electrocatalyst in the form of vertically oriented Fe-doped Ni3S2 nanosheet array grown on three-dimensional (3D)
Ni foam (Fe-Ni3S2/NF), which presented a high
activity and durability for both HER and OER in alkaline media. On
the basis of systematic experiments and calculation, the Fe-doping
was evidenced to increase the electrochemical surface area, improve
the water adsorption ability, and optimize the hydrogen adsorption
energy of Ni3S2, which resulted in the enhancement
of HER activity on Fe-Ni3S2/NF. Moreover, metal
sites of Fe-Ni3S2/NF were proved to play a significant
role in the HER process. During the catalysis of OER, the formation
of Ni–Fe (oxy)hydroxide was observed on the near-surface section
of Fe-Ni3S2/NF, and the introduction of the
Fe element dramatically enhanced the OER activity of Ni3S2. The overall water splitting electrolyzer assembled
by Fe-Ni3S2/NF exhibited a low cell voltage
(1.54 V @ 10 mA cm–2) and a high durability in 1
M KOH. This work demonstrated a promising bifunctional electrocatalyst
for water electrolysis in alkaline media with potential application
in the future.
A solid oxide fuel cell's performance is largely determined by the ionic-conducting electrolyte. A novel approach is presented for using the semiconductor perovskite LaSrTiO (LST) as the electrolyte by creating surface superionic conduction, and the authors show that the LST electrolyte can deliver superior power density, 908.2 mW cm at just 550 °C. The prepared LST materials formed a heterostructure, including an insulating core and a superionic conducting surface layer. The rapid ion transport along the surfaces or grain boundaries was identified as the primary means of oxygen ion conduction. The fuel cell-induced phase transition was observed from the insulating LST to a super O conductivity of 0.221 S cm at 550 °C, leading to excellent current and power outputs.
We developed an advanced surfactant-assistant method for the Ir(x)Sn(1-x)O(2) (0 < x ≤ 1) nanoparticle (NP) preparation, and examined the OER performances by a series of half-cell and full-cell tests. In contrast to the commercial Ir black, the collective data confirmed the outstanding activity and stability of the fabricated Ir(x)Sn(1-x)O(2) (x = 1, 0.67 and 0.52) NPs, which could be ascribed to the amorphous structure, good dispersion, high pore volume, solid-solution state and Ir-rich surface for bi-metal oxides, and relatively large size (10-11 nm), while Ir(0.31)Sn(0.69) exhibited poor electro-catalytic activity because of the separated two phases, a SnO(2)-rich phase and an IrO(2)-rich phase. Furthermore, compared with highly active IrO(2), the improved durability, precious-metal Ir utilization efficiency and correspondingly reduced Ir loading were realized by the addition of Sn component. When the Ir(0.52)Sn(0.48)O(2) cell operated at 80 °C using Nafion® 115 membrane and less than 0.8 mg cm(-2) of the noble-metal Ir loading, the cell voltages we achieved were 1.631 V at 1000 mA cm(-2), and 1.821 V at 2000 mA cm(-2). The IR-free voltage at the studied current density was very close to the onset voltage of oxygen evolution. The only 50 μV h(-1) of voltage increased for the 500 h durability test at 500 mA cm(-2). In fact, these results are exceptional compared to the performances for OER in SPEWE cells known so far. This work highlights the potential of using highly active and stable IrO(2)-SnO(2) amorphous NPs to enhance the electrolysis efficiency, reduce the noble-metal Ir loading and thus the cost of hydrogen production from the solid polymer electrolyte water electrolysis.
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