Rational Design and Engineering of Nanomaterials Derived from Prussian Blue and Its Analogs for Electrochemical Water Splitting.

Electrochemical water splitting (EWS) is a sustainable and promising technology for producing hydrogen as an ideal energy carrier to address environmental and energy issues. Developing highly-efficient electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is critical for increasing the efficiency of water electrolysis. Recently, nanomaterials derived from Prussian blue (PB) and its analogs (PBA) have received increasing attention in EWS applications owing to their unique composition and structure properties. In this Minireview, the latest progress of PB/PBA-derived materials for EWS is presented. Firstly, the catalyst design principles and the advantages of preparing electrocatalysts with PB/PBA as precursors are briefly introduced. Then, strategies for enhancing the electrocatalytic performance (HER, OER or overall water splitting) were discussed in detail, and the recent development and applications of PB/PBA-derived catalysts for EWS were summarized. Finally, major challenges and possible future trends related to PB/PBA-derived functional materials are proposed.

Restricting Growth of Ni3Fe Nanoparticles on Heteroatom-Doped Carbon Nanotube/Graphene Nanosheets as Air-Electrode Electrocatalyst for Zn-Air Battery.

Exploring bifunctional oxygen electrode catalysts with efficient and stable oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) performance is one of the limitations for high-performance zinc-air battery. In this work, Ni3Fe alloy nanoparticles incorporated in three-dimensional (3D) carbon nanotube (CNT)/graphene nanosheet composites with N and S codoping (Ni3Fe/N-S-CNTs) as bifunctional oxygen electrode electrocatalysts for zinc-air battery. The main particle size of Ni3Fe nanoparticles could be well restricted because of the unique 3D structure of carbon nanotube/graphene nanosheet composites (N-S-CNTs). The large specific area of N-S-CNTs is conducive to the uniform dispersion of Ni3Fe nanoparticles. On the basis of the synergistic effect of Ni3Fe nanoparticles with N-S-CNTs, and the sufficient exposure of reactive sites, the synthesized Ni3Fe/N-S-CNTs catalyst exhibits excellent OER performance with a low overpotential of 215 mV at 10 mA cm-2, and efficient ORR activity with a half-wave potential of 0.877 V. When used as an electrocatalyst in zinc-air battery, the device exhibits a power density of 180.0 mW cm-2 and long term durability for 500 h.

Hyperporous-Carbon-Supported Nonprecious Metal Electrocatalysts for the Oxygen Reduction Reaction.

Highly porous carbonaceous nonprecious metal catalysts for the oxygen reduction reaction are prepared by carbonization of low-cost metalloporphyrin-based hyper-crosslinked polymers (MPH-X). With high surface area (2768 m2 g-1 ), hierarchical porous structure, and high metal loading (9.97 wt %), the obtained hyperporous carbon MPH-Fe/C catalyst exhibits high oxygen reduction reaction (ORR) activity with a half-wave potential (0.816 V) that is comparable to the 0.819 V of commercial Pt/C. Stability tests reveal that MPH-Fe/C also exhibits outstanding long-term durability and methanol tolerance. Our findings may offer an alternative approach to produce nonprecious metal ORR catalysts on a large scale owing to the low-cost MPH-X precursors with diverse metal types.

Highly Nitrogen-Doped Three-Dimensional Carbon Fibers Network with Superior Sodium Storage Capacity.

Inspired by the excellent absorption capability of spongelike bacterial cellulose (BC), three-dimensional hierarchical porous carbon fibers doped with an ultrahigh content of N (21.2 atom %) (i.e., nitrogen-doped carbon fibers, NDCFs) were synthesized by an adsorption-swelling strategy using BC as the carbonaceous material. When used as anode materials for sodium-ion batteries, the NDCFs deliver a high reversible capacity of 86.2 mAh g-1 even after 2000 cycles at a high current density of 10.0 A g-1. It is proposed that the excellent Na+ storage performance is mainly due to the defective surface of the NDCFs created by the high content of N dopant. Density functional theory (DFT) calculations show that the defect sites created by N doping can strongly "host" Na+ and therefore contribute to the enhanced storage capacity.

Porous Structured Ni-Fe-P Nanocubes Derived from a Prussian Blue Analogue as an Electrocatalyst for Efficient Overall Water Splitting.

Exploring nonprecious metal electrocatalysts to replace the noble metal-based catalysts for full water electrocatalysis is still an ongoing challenge. In this work, porous structured ternary nickel-iron-phosphide (Ni-Fe-P) nanocubes were synthesized through one-step phosphidation of a Ni-Fe-based Prussian blue analogue. The Ni-Fe-P nanocubes exhibit a rough and loose porous structure on their surface under suitable phosphating temperature, which is favorable for the mass transfer and oxygen diffusion during the electrocatalysis process. As a result, Ni-Fe-P obtained at 350 °C with poorer crystallinity offers more unsaturated atoms as active sites to expedite the absorption of reactants. Additionally, the introduction of nickel improved the electronic structure and then reduced the charge-transfer resistance, which would result in a faster electron transport and an enhancement of the intrinsic electrocatalytic activities. Benefiting from the unique porous nanocubes and the chemical composition, the Ni-Fe-P nanocubes exhibit excellent hydrogen evolution reaction and oxygen evolution reaction activities in alkaline medium, with low overpotentials of 182 and 271 mV for delivering a current density of 10 mA cm-2, respectively. Moreover, the Ni-Fe-P nanocubes show outstanding stability for sustained water splitting in the two-electrode alkaline electrolyzer. This work not only provides a facile approach for designing bifunctional electrocatalysts but also further extends the application of metal-organic frameworks in overall water splitting.

Various Structured Molybdenum-based Nanomaterials as Advanced Anode Materials for Lithium ion Batteries.

A facile and scalable solvothermal high-temperature treatment strategy was developed to construct few-layered ultrasmall MoS2 with less than three layers. These are embedded in carbon spheres (MoS2-C) and can be used as advanced anode material for lithium ion batteries (LIBs). In the resulting architecture, the intimate contact between MoS2 surface and carbon spheres can effectively avert aggregation and volume expansion of MoS2 during the lithiation-delithiation process. Moreover, it improves the structural integrity of the electrode remarkably, while the conductive carbon spheres provide quick transport of both electrons and ions within the electrode. Benefiting from this unique structure, the resulting hybrid manifests outstanding electrochemical performance, including an excellent rate capability (1085, 885, and 510 mAh g-1 at 0.5, 2, and 5 A g-1), and a superior cycling stability at high rates (maintaining 100% of the initial capacity following 500 cycles at 0.5 A g-1). Using identical methods, molybdenum carbide and phosphide supported on carbon spheres (Mo2C-C, and MoP-C) were prepared for LIBs. As a result, MoS2-C exhibits outstanding lithium storage capacities due to its specific layered structure. This study investigates large-scale production capabilities of few-layered structure ultrasmall MoS2 for energy storage, and thoroughly compares lithium storage performance of molybdenum compounds.

Hierarchically Porous Electrocatalyst with Vertically Aligned Defect-Rich CoMoS Nanosheets for the Hydrogen Evolution Reaction in an Alkaline Medium.

Effective electrocatalysts for the hydrogen evolution reaction (HER) in alkaline electrolytes can be developed via a simple solvothermal process. In this work, first, the prepared CoMoS nanomaterials through solvothermal treatment have a porous, defect-rich, and vertically aligned nanostructure, which is beneficial for the HER in an alkaline medium. Second, electron transfer from cobalt to MoS2 that reduces the unoccupied d orbitals of molybdenum can also enhance the HER kinetics in an alkaline medium. This has been demonstrated via a comparison of the catalytic performances of CoMoS, CoS, and MoS2. Third, the solvothermal treatment time evidently impacts the electrocatalytic activity. As a result, after 24 h of solvothermal treatment, the prepared CoMoS nanomaterials exhibit the lowest onset potential (42 mV) and overpotential (98 mV) for delivering a current density of 10 mA cm-2 in a 1 M KOH solution. Thus, this study provides a simple method to prepare efficient electrocatalysts for the HER in an alkaline medium.

Highly nitrogen and sulfur dual-doped carbon microspheres for supercapacitors.

Heteroatom doping, especially dual-doped carbon materials have attracted much attention for the past few years, and have been regarded as one of the most efficient strategies to enhance the capacitance behavior of porous carbon materials. In this work, a facile two-step synthetic route was developed to fabricate nitrogen and sulfur co-doped carbon microsphere (NSCM) by using thiourea as dopant. The N/S doping content is controlled via varying the carbonization temperature. It has been proved that a suitable quantity of N and S groups could not only provide pseudo-capacitance but also promote the electron transfer for carbon materials, which ensures the further utilization of the exposed surfaces for charge storage. The optimized NSCM prepared at a carbonization temperature of 800°C (NSCM-800) achieves a capacitance of 277.1Fg-1 at a current density of 0.3Ag-1 in 6.0molL-1 KOH electrolyte, which is 71% higher than that of undoped carbon microsphere. Besides, NSCM-800 shows an excellent cycling stability, 98.2% of the initial capacitance is retained after 5,000 cycles at a current density of 3.0Ag-1.

Nitrogen and sulfur co-doping of 3D hollow-structured carbon spheres as an efficient and stable metal free catalyst for the oxygen reduction reaction.

Three-dimensional, hollow-structured carbon sphere nanocomposites (N,S-hcs) doped with nitrogen and sulfur were prepared using a soft template approach followed by a high-temperature treatment. The synthesized N,S-hcs nanomaterials exhibited favourable catalytic activity for the oxygen reduction reaction (ORR) compared to carbon spheres doped solely with nitrogen (N-hcs), polypyrrole (PPY) solid nanoparticles and irregular fragments of polyaniline (PAN). These results demonstrated the co-doping of N/S and the relatively large surface area of the mesoporous carbon structure that enhanced the catalytic activity of the resulting material. Notably, the prepared N,S-hcs electrocatalysts provided four electron oxygen reduction selectivity, long-term durability and high resistance to methanol poisoning, all of which represented improvements over the conventional Pt/C electrocatalyst. The progress represented by this reported work is of great importance in the development of outstanding non-metal based electrocatalysts for the fuel cell industry.

Pt skin on Pd-Co-Zn/C ternary nanoparticles with enhanced Pt efficiency toward ORR.

Exploring highly active, stable and relatively low-cost nanomaterials for the oxygen reduction reaction (ORR) is of vital importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, a highly active, durable, carbon supported, and monolayer Pt coated Pd-Co-Zn nanoparticle is synthesized via a simple impregnation-reduction method, followed by spontaneous displacement of Pt. By tuning the atomic ratios, we obtain the composition-activity volcano curve for the Pd-Co-Zn nanoparticles and determined that Pd : Co : Zn = 8 : 1 : 1 is the optimal composition. Compared with pure Pd/C, the Pd8CoZn/C nanoparticles show a substantial enhancement in both the catalytic activity and the durability toward the ORR. Moreover, the durability and activity are further enhanced by forming a Pt skin on Pd8CoZn/C nanocatalysts. Interestingly, after 10 000 potential cycles in N2-saturated 0.1 M HClO4 solution, Pd8CoZn@Pt/C shows improved mass activity (2.62 A mg(-1)Pt) and specific activity (4.76 A m(-2)total), which are about 1.4 and 4.4 times higher than the initial values, and 37.4 and 5.5 times higher than those of Pt/C catalysts, respectively. After accelerated stability testing in O2-saturated 0.1 M HClO4 solution for 30 000 potential cycles, the half-wave potential negatively shifts about 6 mV. The results show that the Pt skin plays an important role in enhancing the activity as well as preventing degradation.