Jinfa Chang

An Effective Pd–Ni2P/C Anode Catalyst for Direct Formic Acid Fuel Cells†

The direct formic acid fuel cell is an emerging energy conversion device for which palladium is considered as the state-of-the-art anode catalyst. In this communication, we show that the activity and stability of palladium for formic acid oxidation can be significantly enhanced using nickel phosphide (Ni(2)P) nanoparticles as a cocatalyst. X-ray photoelectron spectroscopy (XPS) reveals a strong electronic interaction between Ni(2)P and Pd. A direct formic acid fuel cell incorporating the best Pd–Ni(2)P anode catalyst exhibits a power density of 550 mWcm(-2), which is 3.5 times of that of an analogous device using a commercial Pd anode catalyst.

Ni2P enhances the activity and durability of the Pt anode catalyst in direct methanol fuel cells

Pt is the state-of-the-art anode catalyst in direct methanol fuel cells. Here we report that Ni2P promotes the activity and stability of Pt in electrochemical methanol oxidation. Nanoparticles of Ni2P and Pt were co-deposited on a carbon support and their activity in electrochemical methanol oxidation was measured by cyclic voltammetry. Among all Pt–Ni2P/C catalysts, the sample with a 30 wt% loading of Ni2P exhibits the highest electrochemical surface area and activity. The activity of the Pt–Ni2P/C-30% catalyst is significantly higher than that of Pt/C, Ni-promoted Pt/C, and P-promoted Pt/C catalysts, revealed by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Accordingly to X-ray photoelectron spectroscopy, there is a partial electron transfer from Ni2P to Pt, which might be an origin of the enhanced catalytic activity of the Pt/Ni2P bimetallic catalyst. The Pt–Ni2P/C-30% was integrated into a direct methanol fuel cell; this fuel cell exhibits a maximum power density of 65 mW cm−2, more than twice of that of an analogous fuel cell using Pt/C as the anode catalyst. The Pt–Ni2P/C-30%-integrated direct methanol fuel cell has also the highest discharge stability among a series of fuel cells with different Pt-based anode catalysts.

Ultrathin cobalt phosphide nanosheets as efficient bifunctional catalysts for a water electrolysis cell and the origin for cell performance degradation

Low-temperature electricity-driven water splitting is an established technology for hydrogen production, yet only few materials are able to catalyze hydrogen and oxygen evolution reactions in the same medium. Herein, ultrathin CoP nanosheets (CoP NS) as durable bifunctional catalysts for electrochemical water splitting are reported. The OER and HER activity for CoP NS/C reaching 10 mA cm−2 needs an overpotential of only 0.277 V and 0.111 V in a basic solution. Whats more, when integrated into a practical anion exchange membrane water electrolysis cell using CoP NS as both anode and cathode catalysts, a current density of 335 mA cm−2 at 1.8 V is achieved, which is rather competitive to the state-of-the-art Pt/IrO2 catalyst. This work would open a new avenue to explore the use of transition metal phosphides as green and attractive bifunctional catalysts toward mass production of hydrogen fuel for applications.

Pt–CoP/C as an alternative PtRu/C catalyst for direct methanol fuel cells

PtRu/C material is one of the most well-known and efficient anode catalysts in direct methanol fuel cells. Nevertheless, new anode catalysts with even higher performance and lower cost are highly demanded for the further development of this fuel cell technology. Herein, we present a CoP-promoted Pt catalyst as a highly active, anti-poisoning and low-Pt loading catalyst for direct methanol fuel cells (DMFCs). The in situ attenuated total reflection surface-enhanced infrared radiation absorption spectroscopy (ATR-SEIRAS) technique revealed that the presence of CoP in the Pt-based catalyst can promote the methanol oxidation to CO2. A maximum power density of 88.5 mW cm−2 is achieved on a fuel cell based on this novel anode catalyst, which is ca. 1.4 times as high as that based on the state-of-the-art commercial PtRu/C catalyst with the same Pt loading. The present work demonstrates that the Pt–CoP/C will be a very competitive alternative to PtRu/C as the promising anode catalyst for the scale-up production of DMFCs in terms of overall performance and cost effectiveness.

Small Addition of Boron in Palladium Catalyst, Big Improvement in Fuel Cell’s Performance: What May Interfacial Spectroelectrochemistry Tell?

Direct formic acid fuel cell (DFAFC) with Pd-based catalyst anode is a promising energy converter to power portable devices. However, its commercialization is entangled with insufficient activity and poor stability of existing anode catalysts. Here we initially report that a DFAFC using facilely synthesized Pd-B/C with ca. 6 at. % B doping as the anode catalyst yields a maximum output power density of 316 mW cm(-2) at 30 °C, twice that with a same DFAFC using otherwise the state-of-the-art Pd/C. More strikingly, at a constant voltage of 0.3 V, the output power of the former cell is ca. 9 times as high as that of the latter after 4.5 h of continuous operation. In situ attenuated total reflection infrared spectroscopy is applied to probe comparatively the interfacial behaviors at Pd-B/C and Pd/C in conditions mimicking those for the DFAFC anode operation, revealing that the significantly improved cell performance correlates well with a substantially lowered CO accumulation at B-doped Pd surfaces.

Ni2P Makes Application of the PtRu Catalyst Much Stronger in Direct Methanol Fuel Cells

PtRu is regarded as the best catalyst for direct methanol fuel cells, but the performance decay resulting from the loss of Ru seriously hinders commercial applications. Herein, we demonstrated that the presence of Ni2 P largely reduces Ru loss, which thus makes the application of PtRu much stronger in direct methanol fuel cells. Outstanding catalytic activity and stability were observed by cyclic voltammetry. Upon integrating the catalyst material into a practical direct methanol fuel cell, the highest maximum power density was achieved on the PtRu-Ni2P/C catalyst among the reference catalysts at different temperatures. A maximum power density of 69.9 mW cm(-2) at 30 °C was obtained on PtRu-Ni2P/C, which is even higher than the power density of the state-of-the-art commercial PtRu catalyst at 70 °C (63.1 mW cm(-2)). Moreover, decay in the performance resulting from Ru loss was greatly reduced owing to the presence of Ni2 P, which is indicative of very promising applications.

Activity of Platinum/Carbon and Palladium/Carbon Catalysts Promoted by Ni2P in Direct Ethanol Fuel Cells

Ethanol is an alternative fuel for direct alcohol fuel cells, in which the electrode materials are commonly based on Pt or Pd. Owing to the excellent promotion effect of Ni2 P that was found in methanol oxidation, we extended the catalyst system of Pt or Pd modified by Ni2 P in direct ethanol fuel cells. The Ni2 P-promoted catalysts were compared to commercial catalysts as well as to reference catalysts promoted with only Ni or only P. Among the studied catalysts, Pt/C and Pd/C modified by Ni2 P (30 wt %) showed both the highest activity and stability. Upon integration into the anode of a homemade direct ethanol fuel cell, the Pt-Ni2 P/C-30 % catalyst showed a maximum power density of 21 mW cm(-2) , which is approximately two times higher than that of a commercial Pt/C catalyst. The Pd-Ni2 P/C-30 % catalyst exhibited a maximum power density of 90 mW cm(-2) . This is approximately 1.5 times higher than that of a commercial Pd/C catalyst. The discharge stability on both two catalysts was also greatly improved over a 12 h discharge operation.

Monocrystalline Ni12P5 hollow spheres with ultrahigh specific surface areas as advanced electrocatalysts for the hydrogen evolution reaction

Monocrystalline Ni12P5 hollow spheres with ultrahigh specific surface areas were prepared by a water-in-oil microemulsion method. The novel structured Ni12P5 catalyst exhibited excellent catalytic activity and stability towards the hydrogen evolution reaction in acidic solutions.

Dispersion-controlled PtCu clusters synthesized with citric acid using galvanic displacement with high electrocatalytic activity toward methanol oxidation

Dispersion-controlled carbon supported PtCu clusters were firstly synthesized using galvanic displacement of Cu/C, in which citric acid worked as the dispersion agent and its concentration was adjusted to form the as-synthesized clusters. It was found that dispersion played a significant role in tuning the activity for methanol electrooxidation.

Sulfur-Doped Nickel Phosphide Nanoplates Arrays: A Monolithic Electrocatalyst for Efficient Hydrogen Evolution Reactions

Searching for cost-efficient electrocatalysts with high catalytic activity and stability for hydrogen generation by means of water electrolysis would make a great improvement on energy technologies field. Herein, we report high-performance hydrogen evolution reaction (HER) electrocatalysts based on sulfur-doped Ni5P4 nanoplate arrays grown on carbon paper (S-Ni5P4 NPA/CP). This ternary, robust, monolithic S-Ni5P4 NPA/CP exhibits remarkable performance for the HER compared to nickel phosphide and nickel sulfide catalysts. The S-Ni5P4 NPA/CP with ∼6% S presents the most promising behavior for water electrolysis applications. Specifically, it shows an onset potential of 6 mV, needing overpotentials (η) of 56 and 104 mV to attain current densities of 10 and 100 mA cm-2 with a Tafel slope of 43.6 mV dec-1. The turnover frequency of 6% S-Ni5P4 NPA/CP is about 0.11 s-1 at overpotential of 100 mV, which is ca. 10 and 40 times that of Ni5P4 NPA/CP and NiS2 NPA/CP, respectively. It also shows remarkable stability and durability in 0.5 M H2SO4 solution. The results indicate that S and P tune the electronic properties mutually and produce an active catalyst phase for the HER. Furthermore, the density functional theory calculations show that S-Ni5P4 NPA/CP exhibits only 0.04 eV of hydrogen adsorption free energy(Δ GH*), which is more suitable than Pt (∼-0.09 eV). We propose that the S-doping not only restrains the surface oxidation and dissolution of S-Ni5P4 NPA/CP in acid solution but also reduces the Δ GH*. We believe that our work will provide a new strategy to design transition metal phosphide composite materials for practical applications in catalysis and energy fields.