Lead‐Induced Microstrain in Synthesis and Manipulation of Porous Pyrochlore for Boosting Oxygen Evolution Reaction
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Abstract Pyrochlore ruthenates are highlighted as candidates to replace iridium oxide as oxygen evolution reaction (OER) electrocatalyst, but their designable geometric configurations and composition modulations are hampered by the high‐temperature (≈1100 °C) and long‐time calcination (more than 12 h), which further decreases the technical and economic feasibility. In this work, an energy‐ and time‐saving approach is proposed to prepare pyrochlore yttrium ruthenate at a much lower calcination temperature (600 °C) and shorter calcination time (6 h) just by inducing A‐site substitutions of lead ions (YPRO). The local microstrain derived from Pb provides the surficial compression and extra driving force to overcome the strain energy of phase‐transition resistances and the obtained low‐temperature YPRO exhibits enriched pores, deficient geometries, shortened Ru─O bond, and enlarged Ru─O─Ru bond angle, which further modify the electronic structure, involving of the rearranged band alignment and the eliminated bandgap. The regulated morphologic, geometric, and electronic structures in YPRO synergically boost the electrocatalytic OER performance (4.8‐fold and 30.0‐fold enhancements compared with pyrochlore yttrium ruthenate and commercial iridium dioxide (IrO 2 ), respectively) in universal pH conditions. This substitution‐induced strain engineering on phase transition should also be effective for other high‐temperature materials and trigger their diverse intriguing properties.Keywords:
Oxygen evolution
The rational design and synthesis of highly efficient electrocatalysts for oxygen evolution reaction (OER) is of critical importance to the large-scale production of hydrogen by water electrolysis. Here, we develop a bimetallic, synergistic, and highly efficient Co-Fe-P electrocatalyst for OER, by selecting a two-dimensional metal-organic framework (MOF) of Co-ZIF-L as the precursor. The Co-Fe-P electrocatalyst features pronounced synergistic effects induced by notable electron transfer from Co to Fe, and a large electrochemical active surface area achieved by organizing the synergistic Co-Fe-P into hierarchical nanosheet arrays with disordered grain boundaries. Such features facilitate the generation of abundant and efficiently exposed Co3+ sites for electrocatalytic OER and thus enable Co-Fe-P to deliver excellent activity (overpotential and Tafel slope as low as 240 mV and 36 mV dec-1, respectively, at a current density of 10 mA cm-2 in 1.0 M KOH solution). The Co-Fe-P electrocatalyst also shows great durability by steadily working for up to 24 h. Our work thus provides new insight into the development of highly efficient electrocatalysts based on nanoscale and/or electronic structure engineering.
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A highly active and robust electrocatalyst for the oxygen evolution reaction (OER) in acidic conditions is essential for proton-exchange membrane water electrolyzers. Herein, a novel Nd6Ir2O13 electrocatalyst was synthesized and first applied in acidic OER. During the OER, surface Nd atoms are leached out to form active hydrated IrOx; meanwhile, the coordination environment of Ir remains relatively stable. Benefiting from the low Ir content (26.4 wt %), Nd6Ir2O13 affords an Ir mass activity of 123.5 mA per mgIr at an overpotential of 300 mV, about 42-fold that of IrO2. Notably, Nd6Ir2O13 needs an ultralow overpotential of 291 mV to acquire a current density of 10 mA cm–2 and continuously catalyzes OER for 70,000 s with little overpotential increase, far beyond that of the benchmark IrO2 and most of the electrocatalysts for the acidic OER. This work opens a new type of Ir-based oxides with ultralow Ir content, which expands the acidic OER electrocatalyst family of multimetal oxides.
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Electrochemically Exfoliated β-Co(OH)2 Nanostructures for Enhanced Oxygen Evolution Electrocatalysis
Exploring highly efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is very important for the development of renewable energy conversion and storage systems. Layered metal hydroxides have been studied with great interest owing to their high electrochemical activity and stability toward OER. Herein, we demonstrate an efficient approach to engineer the surface active sites in β-Co(OH)2 for enhanced electrocatalysis of OER. We employ a single-step bipolar electrochemical technique for the exfoliation of pristine β-Co(OH)2(Co(OH)2-Bulk) into thinner and smaller sheets. The as-synthesized Co(OH)2 nanostructures with improved active sites exhibit enhanced electrocatalytic activity toward OER with a very low overpotential of 390 mV at 10 mA cm–2 and a Tafel slope of 57 mV dec–1 in alkaline media. The results provide a promising lead for the development of efficient and economically viable electrode materials for oxygen evolution electrocatalysis.
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Abstract Due to the multistep proton-coupled electron transfer, it remains a huge challenge to accelerate the kinetics of oxygen evolution reaction (OER). Here, we demonstrate that perovskite-type LaCr 0.5 Fe 0.5 O 3 nanoparticles can be used as highly active and stable OER electrocatalysts, where it shows a low overpotential of 390 mV at 10 mA/cm 2 , a small Tafel slope of 114.4 mV/dec and excellent stability with slight current decrease after 20 h, superior than that of their individual counterparts (LaFeO 3 and LaCrO 3 ). This finding confirms that the present hybrid material would be an effective means to electrocatalyst for catalyzing OER.
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Abstract The oxygen evolution reaction (OER) is an important half reaction in many energy conversion and storage techniques. However, the development of a low‐cost easy‐prepared OER electrocatalyst with high mass activity and rapid kinetics is still challenging. Herein, we report the facile deposition of tannin‐NiFe (TANF) complex film on carbon fiber paper (CP) as a highly efficient OER electrocatalyst. TANF gives rapid OER reaction kinetics with a very small Tafel slope of 28 mV dec −1 . The mass activity of TANF reaches 9.17×10 3 Ag −1 at an overpotential of 300 mV, which is nearly 200‐times larger than that of NiFe double layered hydroxide. Furthermore, tannic acid in TANF can be electrochemically extracted under anodic potential, leaving the inorganic composite Ni x Fe 1− x O y H z as the OER‐active species. This work may provide a guide to probing the electrochemical transformation and investigating the reactive species of other metal–organic complexes as heterogeneous electrocatalysts.
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