Encapsulation of bimetallic phosphides into graphitized carbon for pH-universal hydrogen evolution reaction

Exploring nonprecious electrocatalysts for water splitting with high efficiency and durability is critically important.Herein,bimetallic phosphides are encapsulated into graphitized carbon to construct a C@NiCoP composite nanoarray using bimetallic metal-organic framework(MOF) as a self-sacrificial template.The resulting C@NiCoP exhibits superior performance for pH-universal electrocatalytic hydrogen evolution reaction(HER),particularly representing a low overpotential of 46.3 mV at 10 mA cm^(-2) and Tafel slope of 44.1 mV dec^(-1) in alkaline media.The structural characterizations combined with theoretical calculation demonstrate that tailored electronic structure from bimetal atoms and the synergistic effect with graphitized carbon layer could jointly optimize the adsorption ability of hydrogen on active sites in HER process,and enhance the electrical conductivity as well.In addition,the carbon layer served as a protecting shell also prevents highly dispersed NiCoP components from agglomeration and/or loss in harsh media,finally improving the durability.This work thus provides a new insight into optimizing activity and stability of pH-universal electrocatalysts by the nanostructural design and electronic structure modulation.

A self-supported heterogeneous bimetallic phosphide array electrode enables efficient hydrogen evolution from saline water splitting

Hydrogen generation from water splitting is of great prospect for the sustainable energy conversion.However,it is still challenging to explore stable and high-performance electrocatalysts toward hydrogen evolution reaction(HER)from saline water such as seawater due to the chloride corrosion.Herein,we developed a self-supported heterogeneous bimetallic phosphide(Ni_(2)P-FeP)array electrode that possesses excellent HER performance in alkaline saline water with an overpotential of 89 mV at 10 mA·cm^(−2)and long-term stability over 90 h at 200 mA·cm^(−2).The analysis showed that the heterostructure between the interfaces of Ni_(2)P-FeP plays a pivotal role in promoting the activity of catalyst.Moreover,the bimetallic phosphide nanoarrays can be employed as a shield for chlorine-corrosion resistance in the saline water,ensuring the long-term durability of hydrogen generation.When employed for alkaline saline water electrolysis,a current density of 100 mA·cm^(−2)is achieved at cell voltage of 1.68 V.This work presents an effective approach for the fabrication of high-performance electrode for HER in alkaline saline environments.

Recent research progress of bimetallic phosphides-based nanomaterials as cocatalyst for photocatalytic hydrogen evolution

Hydrogen energy(H_(2)) has been considered as the most possible consummate candidates for replacing the traditional fossil fuels because of its higher combustion heat value and lower environmental pollution.Photocatalytic hydrogen evolution(PHE) from water splitting based on semiconductors is a promising technology towards converting solar energy into sustainable H_(2)fuel evolution. Developing high-activity and abundant source semiconductor materials is particularly important to realize highly efficient hydrogen evolution as for photocatalysis technology. However, unmodified pristine photocatalysts are often unable to overcome the weakness of low performance due to their limitations. In recent years, transition metal phosphides(TMPs) were used as valid co-catalysts to replace the classic precious metal materials in the process of photocatalytic reaction owing to their lower cost and higher combustion heat value.What is more, bimetallic phosphides have been also caused widespread concern in H_(2)evolution reaction owing to its much lower overpotential, more superior conductivity, and weaker charge carriers transfer impedance in comparison to those of single metal phosphides. In this minireview, we concluded the latest developments of bimetallic phosphides for a series of photocatalytic reactions. Firstly, we briefly summarize the present loading methods of bimetallic phosphides(BMPs) anchored on the photocatalyst. After that, the H;evolution efficiency based on BMPs as cocatalyst is also studied in detail. Besides, the application of BMPs-based host photocatalyst for H_(2)evolution under dye sensitization effect has also been discussed. At last, the current development prospects and prospective challenges in many ways of BMPs are proposed. We sincerely hope this minireview has certain reference value for great developments of BMPs in the future research.

A co-coordination strategy to realize janus-type bimetallic phosphide as highly efficient and durable bifunctional catalyst for water splitting

In this work,a Janus-type dual-ligand metal-organic frameworks derived bimetallic(Fe,Co)P nanoparticles embedded carbon nanotube(CNT)skeleton(DLD-Fe Co P@CNT)is presented and synthesized via a facile"co-coordination synthesis"strategy.The DLD-Fe Co P@CNT hybrid shows much better performances for OER and HER with much lower Tafel slope of 39.6(57.1)m V dec-1,an overpotential of 286(166)m V@10 m A cm^(-2)and better stability for OER(HER)in 1 M KOH.Being both cathode and anode for water splitting,it requires only a low voltage of 1.67 V to obtain 10 mA cm^(-2)with nearly 100%faradaic efficiency,which is close to Pt/C//RuO_(2)cell.Density functional theory calculations based on the bimetallic phosphide(Fe_(0.3)Co_(0.7)P)model reveal that,compared with the monometallic Fe P or Co P,the enhanced catalytic activities of Fe_(0.3)Co_(0.7)P is mainly manifested in its free energy of H adsorption(GH*)closer to zero,larger binding strength for H2O and higher electrical conductivity.

A novel structure of quasi-monolayered NiCo-bimetal-phosphide for superior electrochemical performance

Bimetallic transition metal phosphides(TMPs)as potential candidates for superior electrochemical performance are still facing great challenges in the controllable preparation of two-dimensional(2 D)structures with high aspect ratio.Herein,a novel structure of quasi-monolayered NiCo-bimetal-phosphide(NiCoP)has been designed and successfully synthesized by the newly developed process combined with ultrasonic-cavitation and phase-transition.This is the first time to break through the controllable preparation of 2 D bimetal-phosphides with a thickness of 0.98 nm in sub-nanoscale.Based on the advantages of 2 D quasi-monolayer structure with dense crystalline-amorphous interface and the reconfigured electronic structure between Ni^(δ+)/Co^(δ+)and P^(δ-),the optimized Ni_(5%)CoP exhibits an outstanding bifunctional performance for electrocatalyzing both hydrogen evolution reaction and oxygen evolution reaction in an alkaline medium.Ni_(5%)CoP presents lower overpotentials and voltage of 84 mV&259 mV and1.48 V at the current density of 10 mA cm^(-2)for HER&DER and overall water splitting,respectively,which are superior to most other reported 2 D bimetal-phosphides.This work provides a new strategy to optimize the performance of electrolytic water for bimetal-phosphates and it may be of significant value in extending the design of other ultrathin 2 D structured catalysts.

Effect of a second metal(Co,Fe, Mo and W) on performance of Ni_2P/SiO_2 for hydrodeoxygenation of methyl laurate

NiP/SiOand bimetallic Ni MP/Si O2(M = Co, Fe, Mo, W; Ni/M atomic ratio=5) catalysts were prepared by the temperature-programmed reduction method. The catalysts and their precursors were characterized by means of UV–Vis DRS, H-TPR, XRD, TEM, CO chemisorption and NH-TPD. Their performance for the deoxygenation of methyl laurate was tested on a fixed-bed reactor. The results show that the main phase was NiP in all catalysts, and M(M = Co, Fe, Mo, W) entered the lattice of NiP forming solid solution. Different from Fe and Co, the introduction of Mo and W into NiP/SiOreduced the phosphide particle size and increased the acid amount. In the deoxygenation reaction, the turnover frequency of methyl laurate increased on the catalysts in the order of NiMoP/SiO, NiP/SiO, Ni WP/Si O2, NiFeP/SiOand NiCoP/SiO, which is influenced by the size of phosphide particles and the interaction between Ni and M(M = Fe, Co, Mo or W). The introduction of the second metal(especially Mo and W) into NiP/SiOpromoted the hydrodeoxygenation pathway. This is mainly attributed to the interaction between Ni and the second metal. Finally, the Ni MoP/SiOcatalyst was tested at 340 oC, 3 MPa, methyl laurate WHSV of 14 h-1and H/methyl laurate molar ratio of 25 for 132 h, and its deactivation took place. We found that the catalyst deactivation mainly resulted from carbonaceous deposit rather than the sintering of metal phosphide crystallites.

3D Network nanostructured NiCoP nanosheets supported on N-doped carbon coated Ni foam as a highly active bifunctional electrocatalyst for hydrogen and oxygen evolution reactions

A highly active bi-functional electrocatalyst towards both hydrogen and oxygen evolution reactions is critical for the water splitting. Herein, a self-supported electrode composed of 3D network nanostructured NiCoP nanosheets grown on N-doped carbon coated Ni foam （NiCoP/NF@NC） has been synthesized by a hydrothermal route and a subsequent phosphorization process. As a bifunctional electrocatalyst, the NiCoP/NF@NC electrode needs overpotentials of 31.8 mV for hydrogen evolution reaction and 308.2 mV for oxygen evolution reaction to achieve the current density of 10 mA·cm^-2 in 1 mol·L^-1 KOH electrolyte. This is much better than the correspond- ing monometal catalysts of CoP/NF@NC and NiP/ NF@NC owing to the synergistic effect. NiCoP/NF@NC also exhibits low Tafel slope, and excellent long-term stability, which are comparable to the commercial noble catalysts of Pt/C and RuO2.

Hierarchical NiMoP_(2)-Ni_(2)P with amorphous interface as superior bifunctional electrocatalysts for overall water splitting

Producing highly efficient bifunctional catalyst for the generation of hydrogen and oxygen through overall water splitting is an emerging direction in electrocatalysis.Herein,a dandelion-like hierarchical NiMoP_(2)-Ni_(2)P(nanowire/nanoparticle)heterostructure was synthesized for efficient electrochemical water splitting.The NiMoP_(2)-Ni_(2)P heterostructures grown on carbon cloth as a freestanding integrated electrode exhibited excellent oxygen evolution reaction(OER)activity and hydrogen evolution reaction(HER)activities with low overpotentials(258 mV and 53 mV to reach 10 mA cm~(-2)for the OER and HER,respectively),and small Tafel slope(45 mV dec^(-1)and 58 mV dec^(-1)for the OER and HER,respectively).Moreover,the NiMoP_(2)-Ni_(2)P heterostructure can act as both anode and cathode catalysts for overall water splitting with low overall potential of 1.48 V at 10 mA cm~(-2).Density functional theory(DFT)combined with structural probes suggests that the amorphous heterogeneous interfaces play an essential role in enhanced catalytic performance.

DFT-assisted rational design of CoM_(x)P/CC(M=Fe,Mn,and Ni) as efficient electrocatalyst for wide pH range hydrogen evolution and oxygen evolution

Rational design of highly active transition-metal phosphides for electrocatalyzing overall water splitting in a wide pH range assisted by first-principle calculations can efficiently save the developing cost and hence is quite attractive.Under the guidance of density-functional theory(DFT)calculations that the introduction of dopants(Fe,Mn,and Ni)into CoP could promote the hydrogen evolution reaction(HER)performances,a series of binder-free CoM_(x)P/carbon cloth(CC;M=Fe,Mn,and Ni;x=0,0.05,0.2,0.5,and 1)were fabricated.Both experimental measurements and DFT calculations confirm the electronic modulation of dopants.DFT calculations further reveal that the modulated electronic structure promotes the electronic conductivity,favors the adsorption of key species,and consequently promotes the electrochemical performances.As predicted,the bimetallic phosphides demonstrate excellent HER performances in alkaline,acidic,and alkaline simulated seawater solutions and also deliver excellent oxygen evolution reaction(OER)performances,overwhelming the commercial RuO_(2).Benefiting from the modulated electronic structure and the hierarchical structure with massive CoFe0.05P zero-dimensional(0D)quantum dots anchored on two-dimensional(2D)N-doped porous carbon,CoFe0.05P delivered the best HER in four kinds of electrolytes(ƞ10 of 73 mV in an alkaline simulated seawater solution)and OER in two kinds of electrolytes(ƞ10 of 264 mV in an alkaline solution)with excellent stability of 45 h in the alkaline solution.The assembled CoFe0.05P/CC//CoFe0.05P/CC with the electrodes folded by 180°can still maintain a low cell potential of 1.62 V at 10 mA·cm^(−2).This work proves the feasibility of the reported rational design strategy of developing efficient electrocatalysts for overall water splitting in a wide pH range.