Molybdenum Carbide-PtCu Nanoalloy Heterostructures on MOF-Derived Carbon toward Efficient Hydrogen Evolution.

In this study, PtCu-Mo2 C heterostructure with charge redistribution is investigated via first-principles theoretical calculations. Mo2 C can promote the formation of the electron-rich region of PtCu as an active site, displaying an optimized adsorption behavior toward hydrogen in terms of reduced thermodynamic energy barriers. Owing to the attractive density functional theory calculation results, the PtCu-Mo2 C heterostructure is fabricated via carbonization of the unique metal-organic framework (MOF) followed by the replacement reduction reaction for the first time. Owing to its swift kinetics and outstanding specific activity, it exhibits high hydrogen evolution reaction (HER) catalytic activity (26 mV @ 10 mA cm-2 ) and superior mass activity (1 A mgPt -1 at -0.04 V) in acidic media, which is approximately six times that of commercial Pt/C catalysts. The perception of the intrinsic activity origin of the alloy with an excellent structural support can guide the development of Pt-based and other alloy catalysts in future.

Regulative Electronic States around Ruthenium/Ruthenium Disulphide Heterointerfaces for Efficient Water Splitting in Acidic Media.

Theoretical calculations unveil the charge redistribution over abundant interfaces and the enhanced electronic states of Ru/RuS2 heterostructure. The resulting surface electron-deficient Ru sites display optimized adsorption behavior toward diverse reaction intermediates, thereby reducing the thermodynamic energy barriers. Experimentally, for the first time the laminar Ru/RuS2 heterostructure is rationally engineered by virtue of the synchronous reduction and sulfurization under eutectic salt system. Impressively, it exhibits extremely high catalytic activity for both OER (201 mV @ 10 mA cm-2 ) and HER (45 mV @ 10 mA cm-2 ) in acidic media due to favorable kinetics and excellent specific activity, consequently leading to a terrific performance in acidic overall water splitting devices (1.501 V @ 10 mA cm-2 ). The in-depth insight into the internal activity origin of interfacial effect could offer precise guidance for the rational establishment of hybrid interfaces.

Effects of Intrinsic Pentagon Defects on Electrochemical Reactivity of Carbon Nanomaterials.

Theoretical calculations reveal that intrinsic pentagons in the basal plane can contribute to the local electronic redistribution and the contraction of band gap, making the carbon matrix possess superior binding affinity and electrochemical reactivity. To experimentally verify this, a pentagon-defect-rich carbon nanomaterial was constructed by means of in situ etching of fullerene molecules (C60 ). The electrochemical tests show that, relative to hexagons, such a carbon-based material with abundant intrinsic pentagon defects makes much greater contribution to the electrocatalytic oxygen reduction activity and electric double layer capacitance. It shows a four-electron-reaction mechanism similar to commercial Pt/C and other transition-metal-based catalysts, and a higher specific capacitance than many reported metal-free carbon materials. These results show the influence of intrinsic pentagon defects for developing carbon-based nanomaterials toward energy conversion and storage devices.

Defective N/S-Codoped 3D Cheese-Like Porous Carbon Nanomaterial toward Efficient Oxygen Reduction and Zn-Air Batteries.

Developing a facile and cost-efficient method to synthesize carbon-based nanomaterials possessing excellent structural and functional properties has become one of the most attractive topics in energy conversion and storage fields. In this study, density functional theory calculation results reveal the origin of high oxygen reduction reaction (ORR) activity predominantly derived from the synergistic effect of intrinsic defects and heteroatom dopants (e.g., N, S) that modulate the bandgap and charge density distribution of carbon matrix. Under the guidance of the first-principle prediction, by using ultralight biomass waste as precursor of C, N, and S elements, a defect-rich and N/S dual-doped cheese-like porous carbon nanomaterial is successfully designed and constructed. Herein, the intrinsic defects are artfully generated in terms of alkaline and ammonia activation. The electrochemical measurements display that such a material owns a comparable ORR activity (E1/2  = 0.835 V) to the commercial Pt/C catalyst, along with splendid durability and methanol tolerance in alkali media. Furthermore, as cathode catalyst, it displays a high Zn-air battery performance. The excellent ORR activity of the catalyst can be attributed to its unique 3D porous architecture, abundant intrinsic defects, and high-content active heteroatom dopants in the carbon matrix.

Single-Atom Catalysts for Electrochemical Hydrogen Evolution Reaction: Recent Advances and Future Perspectives.

Hydrogen, a renewable and outstanding energy carrier with zero carbon dioxide emission, is regarded as the best alternative to fossil fuels. The most preferred route to large-scale production of hydrogen is by water electrolysis from the intermittent sources (e.g., wind, solar, hydro, and tidal energy). However, the efficiency of water electrolysis is very much dependent on the activity of electrocatalysts. Thus, designing high-effective, stable, and cheap materials for hydrogen evolution reaction (HER) could have a substantial impact on renewable energy technologies. Recently, single-atom catalysts (SACs) have emerged as a new frontier in catalysis science, because SACs have maximum atom-utilization efficiency and excellent catalytic reaction activity. Various synthesis methods and analytical techniques have been adopted to prepare and characterize these SACs. In this review, we discuss recent progress on SACs synthesis, characterization methods, and their catalytic applications. Particularly, we highlight their unique electrochemical characteristics toward HER. Finally, the current key challenges in SACs for HER are pointed out and some potential directions are proposed as well.

Phosphorization engineering ameliorated the electrocatalytic activity for overall water splitting on Ni3S2 nanosheets.

Phosphorization engineering is an alternative method to explore highly efficient electrocatalysts for water splitting. Herein, a heterostructure consisting of Ni2P and Ni3S2 supported on commercial nickel foam (Ni3S2-Ni2P/NF) was prepared through the conversion of some Ni3S2 molecules into Ni2P by phosphorization engineering. Electrochemical tests revealed that the partial phosphorization of Ni3S2 effectively enhanced the catalytic activity of the host electrocatalyst towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 1 M KOH; in particular, the Ni3S2-Ni2P/NF electrode exhibited the current density of 50 mA cm-2 at the very low OER overpotential of 287 mV and needed the low overpotential of 130 mV to afford 10 mA cm-2 for the HER. Moreover, the alkaline electrolyzer assembled by two Ni3S2-Ni2P/NF electrodes could deliver 10 mA cm-2 at the low voltage of 1.58 V and exhibited excellent durability during electrolysis for 15 h. Therefore, our study opens up an attractive fabrication strategy for highly active heterostructure electrocatalysts.

An iron-doped cobalt phosphide nano-electrocatalyst derived from a metal-organic framework for efficient water splitting.

The development of hydrogen energy relies to a large extent on the electrocatalysts that are highly efficient and widely sourced. Although transition metal phosphides (TMPs) have made great achievements in reducing the overpotential of hydrogen evolution reaction (HER), improving oxygen evolution reaction (OER) performance that is relatively lagging in view of relatively large overpotentials and high kinetics energy barriers is yet to be achieved. Herein, we propose an extremely convenient and practical approach to prepare iron-doped cobalt phosphide nanoparticles (Fe-CoxP NPs) via a one-step method by introducing an iron element in the in situ synthesis of a metal-organic framework (ZIF-67) and then subjecting to a phosphate treatment. The as-obtained Fe-CoxP showed an excellent OER and acceptable HER activities. In particular, for OER, the optimized Fe-doped CoxP (Fe0.27Co0.73P) exhibits an ultra-low overpotential of 251 mV at a current density of 10 mA cm-2, a negligible electrocatalytic degradation after 3000 CV cycles, and time over 40 h-reliant current density stability. When employed as cathode and anode electrodes in water splitting, the current density of 10 mA cm-2 can be achieved at a potential of 1.68 V. Our facile synthetic strategy and innovative ideas are undoubtedly beneficial to the design and construction of advanced water-splitting electrocatalysts.

Co2P quantum dot embedded N, P dual-doped carbon self-supported electrodes with flexible and binder-free properties for efficient hydrogen evolution reactions.

Transition metal phosphides (TMPs) are considered to be superb catalysts for water splitting. In this work, we introduce an efficient strategy to fabricate dicobalt phosphide (Co2P) quantum dots embedded in N, P dual-doped carbon (Co2P@NPC) on carbon cloth (Co2P@NPC/CC) by in situ carbonization of cobalt ion induced phytic acid (PA) and polyaniline (PANI) macromolecule precursors. As a highly efficient self-supported electrode, it has a low onset overpotential (74 mV at 1 mA cm-2) approaching that of the commercial Pt/C catalyst for the hydrogen evolution reaction (HER) in acidic media. Meanwhile, it also shows very low overpotentials of only 116 and 129 mV at 10 mA cm-2 with robust stability in acidic and alkaline media, respectively.

Dual active nitrogen doped hierarchical porous hollow carbon nanospheres as an oxygen reduction electrocatalyst for zinc-air batteries.

Developing non-platinum catalysts for the oxygen reduction reaction (ORR) has become urgent for electrochemical energy devices. Herein, we synthesize N-doped hollow carbon nanospheres (N-HCNs) which only contain active pyridinic-N and graphitic-N by using polystyrene spheres and aniline as the corresponding template and precursor. The electrochemical measurements show that N-HCNs possess superior ORR electrocatalytic activity (half-wave potential is 15 mV higher than that of the precious Pt/C electrocatalyst), durability and anti-toxicity to Pt/C in alkaline media. Simultaneously, N-HCNs also reveal comparable ORR activity and superior stability to Pt/C in acidic media. Such high ORR performance can be ascribed to their hierarchical porous structure, ultra-high specific surface area, plenty of edge defects and high contents of active N atoms. It is noteworthy that when used as the catalyst for the air electrode of zinc-air batteries, N-HCNs present a higher power density and a larger operating voltage than Pt/C at the same discharge current density.

Phytic acid-derivative transition metal phosphides encapsulated in N,P-codoped carbon: an efficient and durable hydrogen evolution electrocatalyst in a wide pH range.

Applications of highly-efficient and durable non-precious metal electrocatalysts for hydrogen evolution reaction (HER) have great potential to relieve the energy crisis. Here, we demonstrate a green method for fabrication of a number of transition metal phosphides (TMPs) by pyrolyzing melamine and self-assembled phytic acid (PA) cross-linked metal complexes. The obtained materials consisting of TMP nanoparticles (NPs) are encapsulated in N,P-codoped carbon (NPC). Among TMPs, the resultant FeP NPs encapsulated in the NPC matrix (FeP NPs@NPC) show the highest HER activity at all pH values. At a current density of 10 mA cm-2, FeP NPs@NPC displays overpotentials of 130, 386 and 214 mV in 0.5 M H2SO4, 1.0 M phosphate buffer solution (PBS) and 1.0 M KOH, respectively. Additionally, the encapsulation by NPC effectively prevents FeP NPs from corrosion, exhibiting almost unfading catalytic activity after 10 h testing in acidic, neutral and basic electrolytes. More importantly, other TMPs wrapped in NPC (CoP NPs@NPC and Ni2P NPs@NPC) can be easily obtained by this method, which also exhibit relatively high activity toward HER. Therefore, this generic synthesis strategy opens a door for unprecedented design and fabrication of novel low-cost TMP based electrocatalysts for HER and other electrochemical applications.

General Strategy for the Synthesis of Transition-Metal Phosphide/N-Doped Carbon Frameworks for Hydrogen and Oxygen Evolution.

Transition metal phosphides (TMPs) have been identified as promising nonprecious metal electrocatalyst for hydrogen evolution reaction (HER) and other energy conversion reactions. Herein, we reported a general strategy for synthesis of a series of TMPs (Fe2P, FeP, Co2P, CoP, Ni2P, and Ni12P5) nanoparticles (NPs) with different metal phases embedded in a N-doped carbon (NC) matrix using metal salt, ammonium dihydrogen phosphate, and melamine as precursor with varying molar ratios and thermolysis temperatures. The resultant TMPs can serve as highly active and durable bifunctional electrocatalyst toward HER and oxygen evolution reaction (OER). In particular, the Ni2P@NC phase only requires an overpotential of ∼138 mV to derive HER in 0.5 M H2SO4, and ∼320 mV for OER in 1.0 M KOH at the current density of 10 mA cm-2. Because of the encapsulation of NC that can effectively prevent corrosion of embedded TMP NPs, Ni2P@NC exhibits almost unfading catalytic performance even after 10 h under both acidic and alkaline solutions. This synthesis strategy provides a new avenue to exploring TMPs as highly active and stable electrocatalyst for the HER, OER, and other electrochemical applications.