Changpeng Liu

Recent advances in catalysts for direct methanol fuel cells

Over the past few decades, direct methanol fuel cells (DMFCs) have been intensively developed as clean and high-efficiency energy conversion devices. However, their dependence on expensive Pt-based catalysts for both the anode and the cathode make them unsuitable for large-scale commercialisation. The essential solution to addressing this shortfall is the development of low-Pt and non-Pt catalysts. Regarding this issue, considerable advances have been made with low-Pt alloys and core-shell-like catalysts, as well as non-platinum Pd–Me, Ru–Se and heat-treated MeNxCy-based catalysts. This perspective reviews potential pathways for increasing the cost-effectiveness and efficiency of these catalysts. Fundamental understanding of the composition–activity and structure–activity relationships, innovative synthesis, and promising developmental directions are highlighted. Regarding durability, the main degradation mechanism of these catalysts and the corresponding mitigating strategies are presented.

Meso/Macroporous Nitrogen‐Doped Carbon Architectures with Iron Carbide Encapsulated in Graphitic Layers as an Efficient and Robust Catalyst for the Oxygen Reduction Reaction in Both Acidic and Alkaline Solutions

Meso-/macroporous nitrogen-doped carbon architectures with iron carbide encapsulated in graphitic layers are fabricated by a facile approach. This efficient and robust material exhibits superior catalytic performance toward the oxygen reduction reaction in both acidic and alkaline solutions and is the most promising alternative to a Pt catalyst for use in electrochemical energy devices.

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.

A Class of High Performance Metal-Free Oxygen Reduction Electrocatalysts based on Cheap Carbon Blacks

For the goal of practical industrial development of fuel cells, cheap, sustainable and high performance electrocatalysts for oxygen reduction reactions (ORR) which rival those based on platinum (Pt) and other rare materials are highly desirable. In this work, we report a class of cheap and high-performance metal-free oxygen reduction electrocatalysts obtained by co-doping carbon blacks with nitrogen and fluorine (CB-NF).The CB-NF electrocatalysts are highly active and exhibit long-term operation stability and tolerance to poisons during oxygen reduction process in alkaline medium. The alkaline direct methanol fuel cell with the best CB-NF as cathode (3 mg/cm2) outperforms the one with commercial platinum-based cathode (3 mg Pt/cm2). To the best of our knowledge, these are among the most efficient non-Pt based electrocatalysts. Since carbon blacks are 10,000 times cheaper than Pt, these CB-NF electrocatalysts possess the best price/performance ratio for ORR, and are the most promising alternatives to Pt-based ones to date.

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.

Available hydrogen from formic acid decomposed by rare earth elements promoted Pd‐Au/C catalysts at low temperature

The usage of hydrogen as a clean, efficient power carrier for stationary and mobile applications is attracting more and more attention. Much effort has been made towards hydrogen application technologies, especially in fuel cells. Nevertheless, the production and storage of hydrogen is the bottleneck of hydrogen economy. In transportable energy applications, hydrogen is generally produced from reforming organic molecules, such as gasoline, methanol, ethanol and so on. Hydrogen production suffers from various problems such as low efficiency, high operating temperature, huge volume, weight loading, and excessive formation of CO. On the other hand, hydrogen storage technologies are limited by low efficiency and possible danger. Notably, formic acid is a promising hydrogen carrier with advantages of considerable hydrogen content (4.4 wt %), and non-toxic and non-flammable properties. It has been reported that Au-based, Pd-based, 10] Pt-based, and metal (e.g. , Ru, Ir, Rh, Fe) complex catalysts can be used for the decomposition of formic acid (DCFA). The hydrogen from the DCFA also has been used in proton exchange membrane fuel cell (PEMFC). 21] In our previous study, the Au or Ag additive overcame the deactivation of Pd catalyst. Furthermore, the addition of Ce further improved the activity of the Pd–Au and Pd–Ag catalysts. Then, it is necessary to understand the promotion effect of other rare earth elements (REs) and design new and highly active catalysts. Here, we systematically studied the promotion effect of three REs (Dy, Eu, and Ho) on the Pd–Au/C catalysts in the DCFA reaction. In addition, the application of reforming gas in fuel cell is studied. Figure 1 a shows the output rates of reforming gas from DCFA catalyzed by Pd–Au/C, Pd–Au–Dy/C, Pd–Au–Eu/C, and Pd–Au–Ho/C. All the REs (Dy, Eu, Ho) could significantly promote the activity of Pd-Au/C catalyst. The activity order of the four catalysts was Pd–Au–Dy/C>Pd–Au–Eu/C>Pd–Au–Ho/C> Pd–Au/C. All activities increased with the temperature exponentially. In addition, these catalysts were even active at room temperature temporarily and above 325 K steadily. The activation energies for the DCFA reaction on the prepared catalysts were also calculated according to the Arrhenius equation. Figure 1 b and Table 1 show that all the REs-promoted Pd–Au/C catalysts have lower activation energies of DCFA than Pd–Au/C. Among the REs catalysts, Pd–Au–Eu/C had the lowest value of 84.2 7.4 kJ mol . However, the most active was Pd–Au–Dy/C, which had a decomposition rate of 1198 mL min 1 g 1 Pd and a turnover frequency (TOF) of 269 202 h 1 at 365 K. This catalytic performance of Pd–Au–Dy/C can provide output power of 106 W g 1 Pd theoretically, which is promising to be used in portable applications. Generally, promotion effect comes from three aspects, that is, distribution improvement of nanoparticles, electronic effect, and synergistic effect. The promotion effect of REs in these three aspects is stated as follows. Firstly, the particle size distributions of the prepared catalysts were measured by transmission electron microscopy (TEM), as shown in Figure 2 A and Figure 2 B. The relationships among the average particle size, activity, TOF, and activation energy are shown in Figure 3. The activity of REs promoted Pd–Au/C catalysts increased from 431 to 1198 mL min 1 g 1 Pd with the size decrease from 4.6 1.5 to 2.0 1.5 nm (Figure 3 a). The activity of REs-promoted catalysts can be improved by decreasing the particle size, likely due to the increasing surface-tovolume ratio. However, the TOF and activation energy Ea are not clearly dependent on the particle size as shown in Figure 3 b and Figure 3 c. Interestingly, Figure 3 d shows that TOF increased with decreasing activation energy, indicating that the activation energy determines the catalytic activity of the Figure 1. a) The activity of Pd–Au/C, Pd–Au–Dy/C, Pd–Au–Eu/C, and Pd–Au– Ho/C catalysts at different temperatures; the activity is expressed by the output gas per minute and per gram Pd. b) lnk vs T 1 plot for the DCFA reaction according to Arrhenius equation. The activation energies are shown in Table 1.

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.

Enhanced activity of Pt nano-crystals supported on a novel TiO2@N-doped C nano-composite for methanol oxidation reaction

The development of advanced support materials displays the potential for both reducing the cost and simultaneously increasing the activity of catalysts. In the current work, a novel N-doped carbon coated hydrophilic titanium dioxide (TiO2@N-doped C) nano-composite, constructed by the procedure of an in situ polymerization and subsequent pyrolysis, was utilized to support Pt nano-crystals for the methanol oxidation reaction (MOR). The as-prepared Pt/TiO2@N-doped C catalyst generated 1.74-fold higher activity, 2.08-fold higher stability and much better resistance to CO poisoning than a commercial state-of-the-art Pt/C catalyst. The enhanced catalytic performance was ascribed to the improved CO tolerance and the catalyst–support interaction due to the utilization of the TiO2@N-doped C nano-composite, which not only provides rich active –OH groups to promote CO oxidation via the bifunctional mechanism, but also modifies the electronic structure of the Pt NPs to improve the intrinsic kinetics of MOR. The as-developed TiO2@N-doped C nano-composite is a highly promising catalyst support material for use in fuel cell technology.

A modified Nafion membrane with extremely low methanol permeability via surface coating of sulfonated organic silica

We developed a method to significantly decrease the methanol permeability of a Nafion membrane that does not require sacrificing its proton conductivity and mechanical stability. The Nafion membrane modified by the coating of a thin layer of sulfonated organic silica on the membrane surface exhibits significantly decreased methanol permeability--the permeability is decreased to an undetectable level--while retaining an acceptable ionic conductivity of 0.029 S cm(-1).

Enhanced Catalytic Performance of Composition‐Tunable PtCu Nanowire Networks for Methanol Electrooxidation

Ultrathin PtCux (x=1, 2 and 3) nanowire networks (NWMs) with controllable compositions were successfully synthesized by using Triton X‐100 as the structure‐directing agent in aqueous solution. The as‐prepared PtCux nanocrystals were characterized by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, cyclic voltammetry, and chronoamperometry. The results show that electrocatalytic performance of the PtCux NWNs towards the methanol oxidation reaction is enhanced relative to that of commercial Pt/C catalysts. Moreover, if the initial atomic ratio of Pt/Cu is 1:2, the corresponding PtCu2 NWNs catalyst generates mass activity that is 3.77‐fold higher and specific activity that is 2.71‐fold higher than the corresponding properties of commercial Pt/C catalysts. The enhanced activity can be attributed to a unique structure and a modified electronic effect.