Understanding the Surface Reconstruction on Ternary Wx CoBx for Water Oxidation and Zinc-Air Battery Applications.

Here, the synthesis of a series of pure phase metal borides is reported, including WB, CoB, WCoB, and W2 CoB2 , and their surface reconstruction is studied under the electrochemical activation in alkaline solution. A cyclic voltammetric activation is found to enhance the activity of the CoB and W2 CoB2 precatalysts due to the transformation of their surfaces into the amorphous CoOOH layer with a thickness of 3-4 nm. However, such surface transformation does not happen on the WB and WCoB due to their superior structure stability under the applied voltage, highlighting the importance of metal components for the surface reconstruction process. It is found that, compared with CoB, the W2 CoB2 surface shows a quicker reconstruction with a larger active surface area due to the selective leaching of the W from its surface. In the meantime, the metallic W2 CoB2 core underneath the CoOOH layer shows a better promotion of its oxygen evolution reaction (OER) performance than CoB. Therefore, the ternary W2 CoB2 shows better OER performance than the CoB, as well as the WB and WCoB. It is also found that the mixture of W2 CoB2 with Pt/C as the catalysts in air electrode for rechargeable Zn-air battery (ZAB), shows better performance than the IrO2 -Pt/C couple-based ZAB.

Tellurium Triggered Formation of Te/Fe-NiOOH Nanocubes as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting.

The electrocatalyzed oxygen and hydrogen evolution reactions (OER/HER) are the key constituents of water splitting toward hydrogen production over electrolysis. The development of stable non-noble nanomaterials as bifunctional OER/HER electrocatalysts is the foremost bottleneck to commercial applications. Herein, the fabrication of Te-modulated FeNiOOH nanocubes (NCs) by a novel tailoring approach is reported, and the doping of Te superbly modulated the local electronic structures of Fe and Ni. The Te/FeNiOOH-NC catalyst displays better mass and electron transfer ability, exposure of plentiful OER/HER edge active centers on the surface, and a modulated electronic structure. Accordingly, the as-made Te/FeNiOOH-NC catalyst reveals robust OER activity (overpotential of 0.22 V@10 mA cm-2) and HER activity (overpotential of 0.167 V@10 mA cm-2) in alkaline media. Considerably, this bifunctional catalyst facilitates a high-performance alkaline water electrolyzer with a cell voltage of 1.65 V at 10 mA cm-2. This strategy opens up a new way for designing and advancing the tellurium dopant nanomaterials for various applications.

Nano-engineering of prussian blue analogues to core-shell architectures: Enhanced catalytic activity for zinc-air battery.

To substitute precious metal with non-precious electrocatalysts, that can work efficiently, still remains a great challenge. Herein, we fabricated the series of nitrogen doped carbon (NC) and CoFe-NC core-shell architectures to produce dual-functionality towards oxygen reduction/evolution reactions and ultimately for Zn-air battery. The addition of NC tends to prevent the reduction of Co/Fe nanoparticles during pyrolysis which not only provide improved catalytic sites but also boost the specific surface area, graphitization degree, electron and mass transfer capacity. With distinctive core-shell morphology, the as-synthesized CoFe-NC/NC shows superior OER performance with low overpotential (270 mV) than IrO2 (340 mV) at 10 mA cm-2 and nearly close ORR activity with respect to Pt/C. When fabricated as zinc-air battery application, CoFe-NC/NC shows 58 mW cm-2 higher peak power density than that of air-cathodes made of Pt/C and IrO2. Further, our catalyst shows good durability due to the synergistic effect of Fe/Co and NC shell.

High temperature self-assembly one-step synthesis of a structurally ordered PtFe catalyst for the oxygen reduction reaction.

Herein, we present a high-temperature self-assembly strategy that directly allows the transformation of adsorbed Pt(NH3)42+ and Fe3+ sources into structurally ordered face-centered tetragonal (fct)-PtFe alloy NPs (2.6 ± 0.2 nm) by integrating reduction and phase transformation. The small-size and ordered atomic arrangement of the fct-PtFe alloy NPs, together with their robust NC protective shell, make these NPs exhibit excellent catalytic activity and stability for the oxygen reduction reaction.

Ultrahigh-Loading Zinc Single-Atom Catalyst for Highly Efficient Oxygen Reduction in Both Acidic and Alkaline Media.

Atomically dispersed Zn-N-C nanomaterials are promising platinum-free catalysts for the oxygen reduction reaction (ORR). However, the fabrication of Zn-N-C catalysts with a high Zn loading remains a formidable challenge owing to the high volatility of the Zn precursor during high-temperature annealing. Herein, we report that an atomically dispersed Zn-N-C catalyst with an ultrahigh Zn loading of 9.33 wt % could be successfully prepared by simply adopting a very low annealing rate of 1° min-1 . The Zn-N-C catalyst exhibited comparable ORR activity to that of Fe-N-C catalysts, and significantly better ORR stability than Fe-N-C catalysts in both acidic and alkaline media. Further experiments and DFT calculations demonstrated that the Zn-N-C catalyst was less susceptible to protonation than the corresponding Fe-N-C catalyst in an acidic medium. DFT calculations revealed that the Zn-N4 structure is more electrochemically stable than the Fe-N4 structure during the ORR process.

Three-Dimensional Fe,N-Decorated Carbon-Supported NiFeP Nanoparticles as an Efficient Bifunctional Catalyst for Rechargeable Zinc-O2 Batteries.

The electro-catalyzed oxygen reduction and evolution reactions (ORR/OER) are the key elements of many energy conversion systems, such as fuel cells, water electrolyzers, and rechargeable metal-air batteries. Structural design of durable non-noble nanomaterials as bifunctional OER/ORR catalysts is a major drawback to commercial applications. Herein, we exposed a strongly coupled hybrid material comprising of NiFeP-cubes nanoparticles supported on three-dimensional interconnected Fe,N-decorated carbon (3D-FeNC) as a robust bifunctional ORR/OER catalyst. The strongly coupled NiFeP@3D-FeNC catalyst shows better electron and mass transfer capability, exposure of abundant ORR/OER active sites on the surface, and strongly coupled effects. Accordingly, the as-prepared NiFeP@3D-FeNC catalyst exhibits robust ORR activity (half-wave potential of 0.84 V vs reversible hydrogen electrode) and OER performance (over-potential 0.25 V@10 mA cm-2) in alkaline media. Significantly, the oxygen electrode prepared from the NiFeP@3D-FeNC catalyst further demonstrated superior charge/discharge behavior and long-lasting rechargeability than the benchmark Pt/C + IrO2 catalyst in rechargeable zinc-O2 batteries. This approach opens up a new avenue for the synthesis and advanced the hybrid nanomaterials for various applications.