Enhancing Ni/Co Activity by Neighboring Pt Atoms in NiCoP/MXene Electrocatalyst for Alkaline Hydrogen Evolution.

Density functional theory (DFT) calculations demonstrate neighboring Pt atoms can enhance the metal activity of NiCoP for hydrogen evolution reaction (HER). However, it remains a great challenge to link Pt and NiCoP. Herein, we introduced curvature of bowl-like structure to construct Pt/NiCoP interface by adding a minimal 1 ‰-molar-ratio Pt. The as-prepared sample only requires an overpotential of 26.5 and 181.6 mV to accordingly achieve the current density of 10 and 500 mA cm-2 in 1 M KOH. The water dissociation energy barrier (Ea) has a ~43 % decrease compared with NiCoP counterpart. It also shows an ultrahigh stability with a small degradation rate of 10.6 µV h-1 at harsh conditions (500 mA cm-2 and 50 °C) after 3000 hrs. X-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and X-ray absorption fine structure (XAFS) verify the interface electron transfer lowers the valence state of Co/Ni and activates them. DFT calculations also confirm the catalytic transition step of NiCoP can change from Heyrovsky (2.71 eV) to Tafel step (0.51 eV) in the neighborhood of Pt, in accord with the result of the improved Hads at the interface disclosed by in situ electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) tests.

Interfaces Decrease the Alkaline Hydrogen-Evolution Kinetics Energy Barrier on NiCoP/Ti3C2Tx MXene.

Heterointerfaces can adjust the adsorption energy with intermediates in the transition state for a much decreased kinetics energy barrier (Ea). One typical transition metal phosphide, NiCoP grains (∼5 nm in size), was anchored on a Ti3C2Tx MXene monolayer (∼1 nm in thickness) to boost the kinetics toward alkaline hydrogen evolution reaction (HER). General electrochemical experiments at different temperatures give a small Ea of 31.4 kJ mol-1, showing a 22.1% decrease compared to its counterpart NiCoP nanoparticles (40.3 kJ mol-1). Impressively, the overpotential of NiCoP@MXene dramatically decreases from 71 mV to 4 mV at 10 mA cm-2 when the temperature increases from 25 °C to 65 °C. On a single NiCoP@MXene sheet, scanning electrochemical microscopy (SECM) tests also give a very close value of Ea = 31.9 kJ mol-1, with a relative error of ∼1.6%. Density functional theory (DFT) calculations confirm the interface between NiCoP and MXene can effectively decrease the energy barrier of water dissociation by 16.0%. The three kinds of studies on macro, micro/nano, and atomic scales disclose the interfaces can reduce the kinetics energy barrier about 16.0-22.1%. Besides, the photothermal effect of MXenes can easily raise the catalyst temperature under vis-NIR light, which has been applied in practical scenarios under sunlight for energy savings.

Engineering 3D hierarchical thorn-like PtPdNiCu alloyed nanotripods with enhanced performances for methanol and ethanol electrooxidation.

Developing efficient and stable electrocatalysts with three-dimensional (3D) hierarchical nanostructures is extremely important in practical applications of direct alcohol fuel cells. Herein, 3D hierarchical thorn-like multi-metallic PtPdNiCu alloyed nanotripods (PtPdNiCu TNTPs) were efficiently fabricated by a one-pot aqueous method, in which Pluronic F127 performed as the structure-director and dispersing agent. The as-prepared PtPdNiCu TNTPs exhibited distinct electrocatalytic activity for methanol oxidation reaction (MOR) with a mass activity (MA) of 1.465 A mg-1Pd, which is superior to commercial Pt/C (0.925 A mg-1Pd) in 1.0 M KOH solution, along with the greater MA (1.019 A mg-1Pd) for ethanol oxidation reaction (EOR) than Pt/C (0.712 A mg-1Pd). This work would provide an impetus for rationally constructing multimetal nanomaterials to commercial implementation of advanced alcohol fuel cells.

Well-dispersed Co3Fe7 alloy nanoparticles wrapped in N-doped defect-rich carbon nanosheets as a highly efficient and methanol-resistant catalyst for oxygen-reduction reaction.

To explore alkaline fuel cells in practice, searching low-cost and efficient alternatives to Pt-based catalysts is urgent yet challenging for oxygen reduction reaction (ORR). Herein, Co3Fe7 alloy nanoparticles wrapped in N-doped defect-rich carbon nanosheets (Co3Fe7/CNs) were synthesized at 800 °C by a one-step pyrolysis of the mixture (dicyandiamide, iron (II) phthalocyanine (FePc), cobalt (II) phthalocyanine (CoPc) and Fe2O3), defined as Co3Fe7/CNs-800 for simplicity. The pyrolysis temperature and the dosages of dicyandiamide closely correlated to the ORR performance of the resultant catalysts in 0.1 M KOH solution. Significantly, the optimized Co3Fe7/CNs-800 exhibited encouraging onset potential (Eonset = 0.97 V) and half-wave potential (E1/2 = 0.85 V) in the alkaline media, surpassing commercial Pt/C (50 wt%, Eonset = 0.96 V, E1/2 = 0.84 V). This work provides a feasible strategy for developing efficient non-noble metal ORR electrocatalysts in the alkaline condition.

Simple fabrication of trimetallic platinum-nickel-cobalt hollow alloyed 3D multipods for highly boosted hydrogen evolution reaction.

Alkaline hydrogen evolution reaction (HER) electrocatalysts with high catalytic activity and long-term durability are of significance for sustainable energy applications. Herein, we prepared trimetallic PtNiCo hollow alloyed 3D multipods (HAMPs) with rough surfaces by an effective one-pot solvothermal strategy coupled with acid etching, as evidenced by a series of characterizations. By virtue of the trimetals and unique structures, the PtNiCo HAMPs exhibited excellent HER performance in 1.0 M KOH electrolyte with a low overpotential (η, 20 mV) and small Tafel slope (46.3 mV dec-1), superior to homemade PtNi HAMPs, PtCo nanocrystals (NCs) and commercial Pt/C catalysts. This study provides some constructive guidelines for synthesis of advanced hollow multimetallic catalysts in energy systems.

Porous dendritic PtRuPd nanospheres with enhanced catalytic activity and durability for ethylene glycol oxidation and oxygen reduction reactions.

Developing highly active and durable catalyst is of pivotal importance in fuel cells, owing to excessive consumption of fossil fuels. Herein, porous dendritic PtRuPd nanospheres (PtRuPd NSs) were synthesized by a facile hexadecylpyridinium chloride (HDPC)-mediated one-pot aqueous method with ascorbic acid (AA) as the reducing agent. The as-obtained PtRuPd NSs displayed high-efficient catalytic activity and durability for ethylene glycol oxidation reaction (EGOR) and oxygen reduction reaction (ORR). It exhibited enlarged mass activity (MA, 1.368 A mg-1) compared to commercial Pt/C (1.100 A mg-1) for EGOR. Besides, the onset potential (Eonset, 0.930 V) and half-wave potential (E1/2, 0.852 V) of PtRuPd NSs were more positive relative to homemade PtPd NSs (0.905 and 0.840 V), PdRu NSs (0.895 and 0.839 V), and commercial Pt/C (0.910 and 0.822 V) toward ORR. This work provides some valuable guidelines for producing novel trimetallic nanocatalysts in fuel cells.

Flower-like platinum-cobalt-ruthenium alloy nanoassemblies as robust and highly efficient electrocatalyst for hydrogen evolution reaction.

Exploring hydrogen evolution reaction (HER) catalyst with highly catalytic features in alkaline conditions is considered as significance for water splitting. In this study, a general and simple method was developed to prepare flower-like platinum-cobalt-ruthenium alloy nanoassemblies (PtCoRu NAs) by using murexide and cetyltrimethylammonium chloride (CTAC) as the co-structure-directing agents. Benefiting from the structural advantages and multimetallic compositions, the as-prepared PtCoRu NAs displayed remarkably enhanced electrocatalytic performance for the HER in 1.0 M KOH, with a low overpotential (η, 22 mV) to drive 10 mA cm-2, small Tafel slope (46 mV dec-1), and high exchange current density (j0, 3.30 mA cm-2) during the long-term electrolysis. The as-developed strategy sheds some valuable guidelines for preparing advanced multimetallic catalysts for production of hydrogen in fuel cells.

Graphene wrapped Fe7C3 nanoparticles supported on N-doped graphene nanosheets for efficient and highly methanol-tolerant oxygen reduction reaction.

Green and efficient non-precious metal electrocatalysts for oxygen reduction reaction (ORR) are prepared to meet the increasing demand for clean, secure and sustainable energy. Herein, we report a novel and environmentally friendly strategy for synthesis of graphene-wrapped iron carbide (Fe7C3) nanoparticles supported on hierarchical fibrous N-doped graphene with open-mesoporous structures (Fe7C3/NG) by simply annealing the mixture of melamine, iron (II) phthalocyanine (FePc) and Fe2O3. The effects of the pyrolysis temperature and the molar ratio of FePc to melamine were critically examined in the controls. Remarkably, the Fe7C3/NG obtained at 800 °C (i.e. Fe7C3/NG-800) manifested the forward shifts in the onset potential (0.98 V) and half-wave potential (0.85 V) with respective to commercial Pt/C (50 wt%) in 0.1 M KOH, coupled with the great enhancement in the durability (still remained 92.11% of its initial current density even after 40,000 s) and strong methanol tolerance. This research presents a promising strategy for developing Pt-free non-precious efficient ORR electrocatalysts in fuel cells.

Graphene-encapsulated cobalt nanoparticles embedded in porous nitrogen-doped graphitic carbon nanosheets as efficient electrocatalysts for oxygen reduction reaction.

Transition metal and nitrogen (N) doped carbon materials are regarded as promising alternatives to expensive Pt-based catalysts for oxygen reduction reaction (ORR), thanks to their natural abundance, good stability and high energy conversion efficiency. Herein, a facile efficient pyrolysis approach was developed to prepare graphene-encapsulated Co nanoparticles (NPs) embedded in porous nitrogen-doped graphitic carbon nanosheets (Co@G/N-GCNs), in which g-C3N4 served as C and N sources, and cobalt phthalocyanine (CoPc) as the Co- and N-sources. The as-obtained catalyst exhibited exceptional ORR activity (E1/2 = 0.86 V vs. RHE), good durability (12 mV negative shift of E1/2 after 2000 cycles), and strong methanol resistance, surpassing those of commercial Pt/C catalyst in alkaline conditions. The pyrolysis temperature and entrapped contents of metal NPs had critical impacts on the ORR features. This work offers a feasible strategy for designing low-cost non-noble-metal catalysts for energy storage and conversion.

One-pot solvothermal synthesis of three-dimensional hollow PtCu alloyed dodecahedron nanoframes with excellent electrocatalytic performances for hydrogen evolution and oxygen reduction.

It is a great challenge to develop simple approach to construct three-dimensional (3D) bimetallic alloyed nanoframes (NFs) with tunable surface structures, albeit with the availability of noble metal NFs in catalysis. Herein, a one-pot solvothermal method was employed for scalable preparation of uniform hollow PtCu rhombic dodecahedron nanoframes (PtCu RDNFs) in the presence of cetyltrimethylammonium chloride (CTAC), where diglycolamine (DGA) served as the co-reductant and co-structure director. The above architectures had the larger electrochemically active surface area (ECSA, 36.85 m2 g-1Pt) than that of commercial Pt black (15.85 m2 g-1Pt), along with the improved catalytic characters for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in acid electrolytes alternative to those of Pt black. It demonstrates great potential applications of PtCu RDNFs in fuel cells and beyond.