Boron doping induced electronic reconfiguration of Fe-Nx sites in N-doped carbon matrix for efficient oxygen reduction reaction in both alkaline and acidic media

Developing non-precious metal-based catalysts as the substitution of precious catalysts (Pt/C) in oxygen reduction reaction (ORR) is crucial for energy devices. Herein, a template and organic solvent-free method was adopted to synthesize Fe, B, and N doped nanoflake-like carbon materials (Fe/B/N–C) by pyrolysis of monoclinic ZIF-8 coated with iron precursors and boric acid. Benefiting from introducing B into Fe–N–C, the regulated electron cloud density of Fe-N_x sites enhance the charge transfer and promotes the ORR process. The as-synthesized Fe/B/N–C electrocatalyst shows excellent ORR activity of a half-wave potential (0.90 V vs 0.87 V of Pt/C), together with superior long-term stability (95.5% current density retention after 27 h) in alkaline media and is even comparable to the commercial Pt/C catalyst (with a half-wave potential of 0.74 V vs 0.82 V of Pt/C) in an acidic electrolyte. A Zn-air battery assembled with Fe/B/N–C as ORR catalyst delivers a higher open-circuit potential (1.47 V), specific capacity (759.9 mA h g^?1_Zn at 10 mA cm^?2), peak power density (62 mW cm^?2), as well as excellent durability (5 mA cm^?2 for more than 160 h) compared to those with commercial Pt/C. This work provides an effective strategy to construct B doped Fe–N–C materials as nonprecious ORR catalyst. Theoretical calculations indicate that introduction of B could induce Fe-N_x species electronic configuration and is favorable for activation of OH1 intermediates to promote ORR process.     

Efficient MnO and Co nanoparticles coated with N-doped carbon as a bifunctional electrocatalyst for rechargeable Zn-air batteries

Developing the low-cost, durable, and efficient bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) plays an important role in the commercial implementation of the Zn-air batteries. Herein, we design and synthesize the MnO and Co nanoparticles coated with N-doped carbon (MC@NC) as an excellent bifunctional oxygen electrocatalyst. It is found that the optimal MC@NC-0.3 exhibits outstanding ORR performance with a positive half-wave potential of 0.82 V and excellent OER activity with a small overpotential of 360 mV at 10 mA cm⁻². When applied in the liquid Zn-air battery, MC@NC-0.3 displays a high maximum power density of 153 mW cm⁻², a large specific capacity of 776 mAh g⁻¹ and the excellent cycling stability with a negligible increase after 300 h. Furthermore, the fiber-shaped all-solid-state Zn-air battery also displays remarkable stability at high current density. This study offers a facile strategy to construct a high-efficient, low-cost, and durable transitional metal-based bifunctional electrode for renewable energy applications.     

Hollow NH2-MIL-101@TA derived electrocatalyst for enhanced oxygen reduction reaction and oxygen evolution reaction

Non-precious metal-based electrocatalysts with excellent activity and stability are highly desired for the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a tannic acid (TA) etching strategy is used to inhibit the metal aggregation and achieve muti-metal doping. The hollow NH₂-MIL-101@TA derived Fe–N–C catalyst exhibits superior ORR catalytic activity with an E_1/2 of 0.872 V and a maximum output power density of 123.4 mW cm⁻² in Zn-air battery. Since TA can easily chelate with metal ions, Fe/Co–N–C and Fe/Ni–N–C are also synthesized. Fe/Ni–N–C manifests exceptional bifunctional activity with an E_j = 10 of 1.67 V and a potential gap of 0.833 V between E_j = 10 and E_1/2 in alkaline electrolyte, which is 45 mV smaller than Pt/C–IrO₂. The improvement of ORR and OER performance of the catalysts via the simple TA etching and chelation method provides a novel strategy for the design and synthesis of efficient electrocatalysts.     

Effect of synthesis method on the oxygen reduction performance of Co–N–C catalyst

In recent years, Co, N co-doped carbon (Co–N–C) materials as oxygen reduction reaction (ORR) catalysts have attracted great attention because of their good ORR stability as well as decent activity. Co-doped zeolitic imidazolate framework-8 (Co@ZIF-8) as the precursor for synthesizing Co–N–C has attracted great interest recently. Co@ZIF-8 synthesis method may affect the properties of the as-synthesized Co@ZIF-8 precursors, which will surely affect the properties and ORR performance of Co@ZIF-8-derived Co–N–C catalysts. Herein, three methods, viz. room-temperature stirring method, reflux method, and hydrothermal method, were used to synthesize Co@ZIF-8 precursors. Physical characterization shows that the synthesis method has a great influence on the textural properties, composition, and graphitization degree of the as-synthesized Co–N–C catalysts. Electrochemical characterization shows that Co–N–C-R synthesized with reflux method exhibits an onset potential (E_onset) of 0.905 V, a half-wave potential (E_1/2) of 0.792 V and a limiting current density (J_L) of 5.85 mA cm^?2 in acidic media, which are higher than those of Co–N–C–S (E_onset = 0.870 V, E_1/2 = 0.770 V, J_L = 4.71 mA cm^?2) and Co–N–C–H (E_onset = 0.892 V, E_1/2 = 0.785 V, J_L = 4.68 mA cm^?2) synthesized with room-temperature stirring method and hydrothermal method, respectively. The better ORR activity observed on Co–N–C-R can be attributed to its larger graphitization degree and larger mesopore volume. Catalytic stability test shows that Co–N–C-R has negligible activity loss after 5000 potential cycles. This work demonstrates that reflux method is a more suitable method for synthesizing Co–N–C catalysts for ORR.     

Amino functionalized carbon nanotubes supported CoNi@CoO–NiO core/shell nanoparticles as highly efficient bifunctional catalyst for rechargeable Zn-air batteries

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the core reaction processes of rechargeable Zn-air battery (ZAB) cathode. Therefore, exploring a bifunctional catalyst with excellent electrochemical performance, high durability, and low cost is essential for rechargeable ZAB. In this work, amino functionalized carbon nanotubes supported core/shell nanoparticles composed of CoNi alloy core and CoO–NiO shell (CoNi@CoO–NiO/NH₂-CNTs-1) is synthesized through a simple and efficient hydrothermal reaction and calcination method, which shows higher ORR/OER bifunctional catalytic performance than the single metal-based catalyst, such as Ni@NiO/NH₂-CNTs and Co@CoO/NH₂-CNTs. The fabricated bimetallic alloy based catalyst CoNi@CoO–NiO/NH₂-CNTs-3 with the optimized loading content of CoNi@CoO–NiO core/shell nanoparticles, presents the best bifunctional catalytic performance for ORR/OER. Experimental studies reveal that CoNi@CoO–NiO/NH₂-CNTs-3 exhibits the onset potential of 0.956 V and 1.423 V vs. RHE for ORR and OER, respectively. It also exhibits a low overpotential of 377 mV to achieve a 10 mA cm^?2 current density for OER, and positive half-wave potentials of 0.794 V for ORR. And the potential difference between half-wave potential of ORR (E_1/2) and the potential at 10 mA cm^?2 for OER (E_j10) is 0.813 V. In addition, when CoNi@CoO–NiO/NH₂-CNTs-3 is used as an air electrode catalyst of rechargeable ZAB, its maximum power density and open circuit voltage (OCV) can reach 128.7 mW cm^?2 and 1.458 V (The commercially available catalyst of Pt/C–RuO₂ is 88.1 mW cm^?2), which strongly demonstrates that the fabricated catalyst CoNi@CoO–NiO/NH₂-CNTs-3 can be used as a highly efficient bifunctional catalyst for ZABs, and is expected to replace those expensive precious metal electrocatalysts to meet the growing demand for new energy devices.     

Metal-organic framework derived Co@NC/CNT hybrid as a multifunctional electrocatalyst for hydrogen and oxygen evolution reaction and oxygen reduction reaction

Seeking a multifunctional electrocatalyst composed of earth-abundant elements for highly hydrogen and oxygen evolution reaction and oxygen reduction reaction (HER, OER and ORR) is technically imperative for the electrocatalytic applications. Herein, we report HER, OER and ORR electrocatalytic performances of metal-organic framework (MOF) derived cobalt nanoparticles encapsulated in nitrogen-doped carbon and carbon nanotube (Co@NC/CNT). The optimized Co@NC/CNT hybrid shows superior HER and OER activities with a small overpotential of 137 mV and 302 mV at a current density of 10 mA cm⁻², respectively. Furthermore, the Co@NC/CNT as an air-cathode in secondary Zn-air battery demonstrates a confined potential gap of 0.88 V over 200 h and a maximum power density of 53.4 mW cm⁻², which are much better than those of Pt/C. The outstanding performances are attributed to the synergistic effects from Co, and N embedded into carbon and CNT. More importantly, the unique surface structure contributes to expose many active sites for superior catalytic activity through allowing a large number of electrons. These outcomes not only prove a facile approach for the preparation of metals/carbon hybrid but also disclose its huge possible as a multifunctional electrocatalyst for sustainable energy systems.     

Top-down preparation of Ni–Pd–P@graphitic carbon core-shell nanostructure as a non-Pt catalyst for enhanced electrocatalytic reactions

Electrochemical reactions such as the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation reaction (MOR) are essential for energy conversion applications such as water electrolysis and fuel cells. Furthermore, Pt or Ir-related materials have been extensively utilized as electrocatalysts for the OER, ORR, and MOR. To reduce the utilization of precious metals, innovative catalyst structures should be proposed. Herein, we report a bi-metallic phosphide (Ni₂P and PdP₂) structure surrounded by graphitic carbon (Ni–Pd–P/C) with an enhanced electrochemical activity as compared to conventional electrocatalysts. Despite the low Pd content of 3 at%, Ni–Pd–P/C exhibits a low overpotential of 330 mV at 10 mA cm^?2 in the OER, high specific activity (2.82 mA cm^?2 at 0.8 V) for the ORR, and a high current density of 1.101 A mg^?1 for the MOR. The superior electrochemical performance of Ni–Pd–P/C may be attributed to the synergistic effect of the bi-metallic phosphide structure and core-shell structure formed by graphitic carbon.     

Co-based MOF-derived Co/CoN/Co2P ternary composite embedded in N- and P-doped carbon as bifunctional nanocatalysts for efficient overall water splitting

In this work, we developed ternary metallic cobalt-cobalt nitride-dicobalt phosphide composite embedded in nitrogen and phosphorus co-doped carbon (Co/CoN/Co₂P-NPC) as bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-prepared Co/CoN/Co₂P-NPC is achieved by simultaneous annealing and phosphating of a Co–N rich metal-organic frameworks (MOFs) precursor. Compare with the phosphorus-free Co/CoN embedded nitrogen-doped carbon electrocatalyst (Co/CoN-NC), the as-prepared Co/CoN/Co₂P-NPC display superior HER and OER low overpotential of 99 mV and 272 mV at current density of 10 mA cm⁻². When Co/CoN/Co₂P-NPC electrocatalyst is use as bifunctional catalysts in overall alkaline water splitting, it exhibit excellent behaviour with 10 mA cm⁻² current at overall cell potential of 1.60 V. The excellent performance of Co/CoN/Co₂P-NPC electrocatalyst is attributed to the phosphating process that could further enhance synergistic effect, create stronger electronic interactions, and form efficient dual heteroatom doping to optimize the interfacial adhesion within the electrocatalyst. This present work will create more opportunities for the development of new, promising and more active sites electrocatalysts for alkaline electrolysis.     

Promotional effects of trace Ni on its dual-functional electrocatalysis of Co/N-doped carbon nanotube catalysts for ORR and OER

It is still a great challenge for developing efficient dual-functional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The electrocatalysts are critical to enhance the efficiency of metal-air cells and fuel cells. In this study, a one-pot vapor deposition method was used to realize the synchronously dope of N and Ni (trace) into Co/C to form Co–Ni (trace)/N-doped carbon nanotubes (Co–Ni (trace)/NCNTs). An interesting result is that injecting dicyandiamide (DCD) into Ni foam as a precursor led to the in situ formation of NCNTs, with synchronous doping of trace Ni into Co species. The cooperative effects of the Co–Ni (trace) and N-doped carbon nanotubes resulted in superior dual-functional electrocatalytic performance of Co–Ni (trace)/NCNTs for the ORR (half-wave potential E_1/2 vs. RHE: 0.83 V, electron transfer number n: 3.97) and OER (overpotential vs. RHE: 337 mV at 10 mA cm^?2, Tafel slope: 94.0 mV dec^?1). Moreover, the Co–Ni (trace)/NCNTs catalyst showed excellent stability during 20,000 s of durability testing for both ORR and OER. This study provides a feasible strategy for designing efficient nonnoble metal-catalysts for renewable energy conversion devices.     

Bamboo-like N-doped carbon tubes encapsulated Co2P–Fe2P derived from zeolitic imidazolate framework as an efficient trifunctional electrocatalyst for water splitting and Zn-air batteries

The development of high-performance and stable trifunctional electrocatalysts is a pressing challenge for the practical application of water splitting and regenerative Zn-air batteries. Herein, bamboo-like N-doped carbon tubes encapsulated Co₂P–Fe₂P nanoparticles (CoFe-PN/C) was fabricated via a facile template-sacrificial approach by using CoZn-ZIF trapping Fe³⁺ (CoFeZn/C) as the precursor. The incorporation of Fe³⁺ was achieved by the one-pot synthesis approach during crystallization of ZIF, which led to the generation of the unique bamboo-like tube structure under the condition of simultaneous phosphating and carbonization. Benefiting from the large surface area, the optimized electronic structure of active sites and the unique bamboo-like nanotube, the resultant CoFe-PN/C can be used as the trifunctional electrocatalyst possessing a small overpotential at 10 mA cm⁻² for the HER (178 mV) and OER (300 mV), as well as a high half-wave potential of 0.884 V for ORR (40 mV more positive than that of commercial 20 wt% Pt/C). Moreover, the self-designed CoFe-PN/C||CoFe-PN/C alkaline electrolyzer driving 50 mA cm⁻² only need operating potential of 1.84 V and the maximum discharge power density of the CoFe-PN/C-assembled ZABs could achieve 152.0 mW cm⁻², superior to those of Pt/RuO₂ couple. This work will facilitate the development and application of trifunctional electrocatalysts based on bi-transition metallic phosphides for energy conversion and storage technology.     

Covalent organic polymer derived N–doped carbon confined FeNi alloys as bifunctional oxygen electrocatalyst for rechargeable zinc-air battery

N–doped carbon confined FeNi alloys are promising candidate to noble Pt and IrO₂ or RuO₂ for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable zinc-air batteries. However, it is difficult to control the distribution of transition metals in the precursor and electrocatalyst. Herein, we design a covalent organic polymer to realize the uniform distribution of metal, nitrogen and carbon precursors. The structure of the obtained electrocatalyst is FeNi nanoparticles coated with carbon shells dispersed on N-doped multilayer porous carbon (FeNi@NC). The resultant FeNi@NC delivered a half-wave potential for ORR of 0.878 V and a low potential of 1.59 V to achieve 10 mA cm^?2 for OER, which surpasses commercial platinum/carbon and ruthenium dioxide. The outstanding bifunctional properties of FeNi@NC attribute to the synergistic coupling between N-doped carbon shells and dense FeNi nanoparticles. Moreover, the self-made zinc-air battery with FeNi@NC air-cathode displayed an excellent energy density of 137.7 mW cm^?2 as well as cycling stability (100 h, 200 cycles).     

Co–Co3O4 nanostructure with nitrogen-doped carbon as bifunctional catalyst for oxygen electrocatalysis

In view of the development of advanced bi-functional oxygen electrodes for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), herein, we report the synthesis of Co–Co₃O₄ nanostructure encased in N-doped carbon (Co–Co₃O₄/NC) by carbothermal reduction followed by controlled oxidative treatment. The formation of a protective-active oxide layer on the metallic-Co not only facilitated the effective charge separation and transport but also displayed improved stability of Co–Co₃O₄/NC in an alkaline operating condition. The Co–Co₃O₄/NC catalyst afforded 0.810 V overvoltage between ORR and OER in 0.1 M KOH solution, consequently, this lower reversible overvoltage would result in energy saving of around 0.246 V if Co–Co₃O₄/NC is used as an oxygen electrode instead of commercially available 40 wt % Pt/C. Furthermore, in comparison with the use of Pt/C + IrO₂ as an ORR and OER catalyst, respectively the single bi-functional electrocatalyst i.e., Co–Co₃O₄/NC would result in energy saving of around 0.13 V.     

One-step synthesis of carbon-encapsulated nickel phosphide nanoparticles with efficient bifunctional catalysis on oxygen evolution and reduction

As a promising and cost-efficient alternative to noble metal catalysts, transition metal phosphides (TMPs) show highly catalytic performance toward oxygen reduction and evolution reactions (ORR and OER). Mesoporous carbon-coated nickel phosphide (NiP) nanoparticles were successfully synthesized by thermal decomposition at 500 °C under N₂/H₂ (95:5) atmosphere. The NiP/C hybrid exhibits excellent OER/ORR activity. It can generate an OER current density of 10 mA cm^?2 at the overpotential of 0.26 V with a low Tafel slope of 43 mV dec^?1, and produce a limited ORR current density of 5.10 mA cm^?2 at 1600 rpm with a half-wave potential of 0.82 V via a 4-electron pathway. In addition, the OER/ORR catalytic currents remain considerable stable without significant loss for more than 25 h polarization. This work will open up a new avenue to design a bifunctional catalyst with a superior OER/ORR activity and stability, and this cost-efficient strategy will pave the way for the industrial application of the renewable energy technologies.     

Structure-design and synthesis of nickel-cobalt oxide/sulfide/phosphide composite nanowire arrays for efficient overall water splitting

The construction of cost-effective bifunctional electrocatalysts with the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant for efficient overall water splitting. Herein, this work demonstrates a novel strategy for the synthesis of nickel-cobalt oxides/sulfides/phosphides composite (denoted as NiCoO–2P/S) nanoarrays on Ni foam. In this method, Ni–Co bimetallic oxide nanowires on Ni foam were partially phosphorized and sulfurized simultaneously in situ to yield Ni–Co oxide/sulfide/phosphide composite. The NiCoO–2P/S arrays have good interfacial effects and display many holes in the nanowires, giving it the advantage of large accessible surfaces on the nanowires and a beneficial for the release of gas bubbles, resulting in an excellent OER performance with a low overpotential (η) of 254 mV at 100 mA cm^?2 and good HER activity (η₁₀ = 143 mV at 10 mA cm^?2). The electrocatalytic test results demonstrate small Tafel slopes (82 mV dec^?1 for HER, 88 mV dec^?1 for OER) and the satisfying durability in an alkaline electrolyte, indicating that the HER and OER activity was enhanced by the introduction of the Ni/Co sulfides and phosphides into Ni–Co oxides composite nanowires. Furthermore, the as-prepared NiCoO–2P/S catalyst can be used as both the anode and the cathode simultaneously to realize overall water splitting in the two-electrode electrolyzer. This system can be driven at low cell voltages of 1.50 and 1.68 V to achieve current densities of 10 and 100 mA cm^?2, respectively. This work provides an alternative strategy to prepare high-performance bifunctional electrochemical materials and demonstrates the advantages of Ni–Co oxide/sulfide/phosphide composites for water splitting.     

Highly efficient PtCo nanoparticles on Co–N–C nanorods with hierarchical pore structure for oxygen reduction reaction

Developing platinum-based nanoparticles on carbon catalysts with high activity and stability for oxygen reduction reaction (ORR) is of great significance for the practical application of fuel cells. Herein, a synchronous strategy of preparing nano-sized PtCo supported on atomic Co and N co-doped carbon nanorods (PtCo/Co–N–C NR) was developed to replace the conventional method of impregnating Pt sources into ready-made carbon materials, in which metal-organic frameworks (MOFs) with Co and Zn ions of rhombic dodecahedron were first prepared using 2-methylimidazole as building block and then their morphology was transformed into porous nanorods via the reduction of Co ions to Co–B–O complex in the MOFs by NaBH₄; subsequently, Pt was deposited on the Co–Zn MOF nanorods through the displacement reaction of PtCl₆^2- and metallic Co and coordination between MOF and PtCl₆^2-; after pyrolysis and acid-leaching process, highly dispersed PtCo/Co–N–C NR was obtained. Attributed to its unique characteristics of hierarchical pore structure, uniform PtCo alloy nanoparticles with the average size of 7.0 nm and strong supporting interaction effect, the catalyst exhibits high ORR activity and stability with the mass activity of 577.0 mA mg^?1_Pt and specific activity of 1.4 mA cm^?2 at 0.9 V vs RHE in 0.1 M HClO₄, which is about 3.6 times and 3.5 times high than that of commercial Pt/C catalyst respectively. This strategy would provide a flexible route to develop highly active and stable ORR electrocatalysts with various morphologies for optimizing the exposure of active sites.     

One-pot solvothermal synthesis of Co2P nanoparticles: An efficient HER and OER electrocatalysts

Development of an inexpensive electrocatalyst for hydrogen evolution (HER) and oxygen evolution reactions (OER) receives much traction recently. Herein, we report a facile one-pot ethyleneglycol (EG) mediated solvothermal synthesis of orthorhombic Co₂P with particle size ~20–30 nm as an efficient HER and OER catalysts. Synthesis parameters like various solvents, temperatures, precursors ratios, and reaction time influences the formation of phase pure Co₂P. Investigation of Co₂P as an electrocatalyst for HER in acidic (0.5 M H₂SO₄) and alkaline medium (1.0 M KOH), furnishes low overpotential of 178 mV and 190 mV, respectively to achieve a 10 mA cm^?2 current density with a long term stability and durability. As an OER catalyst in 1.0 M KOH, Co₂P shows an overpotential of 364 mV at 10 mA cm^?2 current density. Investigation of Co₂P NP by XPS analysis after OER stability test under alkaline medium confirms the formation of amorphous cobalt oxyhydroxide (CoOOH) as an intermediate during OER process.     

Transitional metal alloyed nanoparticles entrapped into the highly porous N-doped 3D honeycombed carbon: A high-efficiency bifunctional oxygen electrocatalyst for boosting rechargeable Zn-air batteries

Rational development of low-cost, durable and high-performance bifunctional oxygen catalysts is highly crucial for metal-air batteries. Herein, transition metal alloyed FeCo nanoparticles (NPs) embedded into N-doped honeycombed carbon (FeCo@N-HC) was efficiently prepared by a one-step carbonization method in the existence of NH₄Cl and citric acid. Benefiting from the honeycomb-like architectures and the synergistic effects of the FeCo alloy with the doped-carbon matrix, the as-synthesized FeCo@N-HC exhibited outstanding oxygen reduction reaction (ORR) with the more positive onset potential (E_onset = 0.98 V vs. RHE) and half-wave potential (E_1/2 = 0.85 V vs. RHE), coupled with outstanding oxygen evolution reaction (OER) with the lower overpotential (318 mV) at 10 mA cm^?2. Besides, the home-made Zn-air battery has the larger power density of 144 mW cm^?2 than Pt/C + RuO₂ (80 mW cm^?2). This research offers some valuable guidelines for constructing robust oxygen catalysts in clean energy storage and conversion technologies.     

Novel in-situ P-doped metal-organic frameworks derived cobalt and heteroatoms co-doped carbon matrix as high-efficient electrocatalysts

Metal organic frameworks (MOFs) are considered as ideal templates for the synthesis of metal-heteroatom co-doped carbon materials. However, the tedious heteroatoms doping pathways hinders the maximizing of catalytic performances. Herein, we synthesize a series of high-efficient Co and N, P heteroatoms co-doped carbon-based composites by first constructing a novel in-situ P-doped MOF with novel larger N, P-containing ligands and 2-methylimidazole as mixed ligands, and then calcining these MOFs at high temperature. During the pyrolysis process, the generated gases derived from the thermal decomposition of organic ligands are liberated from inner of P-ZIF materials to make the Co–Co₂P@NC-P catalysts become loose and porous. When being used as electrode materials, the optimal Co–Co₂P@NC-P₃-700 catalyst exhibits excellent ORR and OER activity, the ORR performance is superior to the Pt/C catalysts, and the OER performance can be comparable with the commercial RuO₂ catalyst. Moreover, when applied in the assembled primary Zn-air battery, the performances of Co–Co₂P@NC-P₃-700 catalyst can outperform the commercial Pt/C catalysts, exhibiting a high peak power density, specific capacity and a long-term stability. Furthermore, the catalytic active sites of catalysts are carefully investigated in this work.     

Porous Co2P film coated on carbon fiber as highly performance electrocatalyst toward overall water splitting

Designing porous active materials and enhancing their contact with conductive substrates is an effective strategy to improve electrolytic water splitting performance of noble metal-free catalysts. Herein, a facile nanostructured electrode, composed of porous Co₂P films coated on carbon fiber (CF@P–Co₂P), is designed and prepared. The unique three-dimensional interconnected pore structure of Co₂P and the close contact between porous Co₂P and CF not only increase specific surface areas to expose abundant catalytic sites but also stimulate the transport of electron, mass and gaseous products in catalytic process. Benefit from the reasonable electrode structure, the self-supported CF@P–Co₂P electrodes present perfect performance with only needing overpotentials of 107.7/175.5/141.8 mV for hydrogen evolution reaction (HER) in acidic/neutral/alkaline solution and 269.4 mV for oxygen evolution reaction (OER) in alkaline solution to get current density of 20 mA cm^?2. In addition, alkaline electrolyzer equipped with CF@P–Co₂P bifunctional electrodes only needs a cell voltage of 1.657 V to get water-splitting current density of 20 mA cm^?2. Even better, the electrolyzer can continuously electrolyze over 50 h with negligibly decreasing current density and the Faraday efficiency is close to 100% toward both HER and OER.     

In-situ transformation of electrodeposited W–Co oxide to ZnCo2O4 nanoparticles as an effective bifunctional catalysts in Zn-air batteries

W–Co was cathodically electrodeposited on gas diffusion layer (GDL) electrodes for application as a bifunctional catalyst for Zn-air batteries. The electrodes were synthesized galvanostatically at various pH values (4.5 and 7.5) and deposition times (5, 15 and 25 min). Transmission electron microscopy (TEM) analysis showed that the deposits oxidized in contact with air, forming a conformal layer of W–Co oxide with a thickness of ~10 nm. During battery cycling, most of the W dissolved in the electrolyte. The remaining Co oxide agglomerated, forming nanoparticles less than 100 nm in size. Zinc (present in the electrolyte as ZnO) was incorporated into the Co oxide nanoparticles. As such, the conformal layer of W–Co oxide transformed into cubic spinel ZnCo₂O₄ nanoparticles which provided excellent bifunctional catalytic activity. The W in the original deposit acted as a conduit to facilitate formation of the ZnCo₂O₄ nanoparticles. The ZnCo₂O₄ catalyst demonstrated good performance in two-electrode and three-electrode full-cell Zn-air battery tests. In three-electrode tests at 10 mA cm⁻², a round trip efficiency of 62% was achieved, exceeding the efficiency of Pt/Ru–C (61%). The final efficiencies were 59% for the three-electrode configuration (after 100 cycles). A high maximum power density of 216 mW cm⁻² was also achieved.