Recently, Prof. Ruqiang Zou’s Group from the Department of Materials Science and Engineering, College of Engineering developed a new strategy by introducing MOF-derived cobalt phosphide nanoparticles into boron and nitrogen co-doped graphene nanotubes for all pH value electrochemical hydrogen evolution reaction (HER). The results were published in the journal Advanced Energy Materials with the title “Metal–Organic Frameworks Derived Cobalt Phosphide Architecture Encapsulated into B/N Co-Doped Graphene Nanotubes for All pH Value Electrochemical Hydrogen Evolution”.
Hydrogen is believed to be one of the most promising candidates for future clean energy supply, considering that it possesses the highest gravimetric energy density and its only combustion product is water. Hydrogen is currently mainly produced from the electrolysis of water, known as the hydrogen evolution reaction. Another advantage of hydrogen over other clean energy sources is its wide supply of electrolytes including various acid and basic electrolytes, industry and domestic waste waters, and even sea water. Traditionally, noble metal Pt is regarded as the best electrocatalyst to accelerate the kinetics in HER. Unfortunately, its commercial applications are impeded by scarcity, high cost and poor stability, as well as low performance in neutral and basic electrolytes.
Motivated by these several challenges, the search for cost-effective and highly efficient catalysts with large earth abundance and long stability has been made of immense significance toward earth-enriched metal for HER electrocatalysts. Transition metal phosphide (TMP) based electrocatalysts have been broadly applied for HER activity. Among the existing myriad of TMP, cobalt phosphide (CoP) has been identified as a promising candidate for HER as compared to iron, copper, nickel, and tungsten phosphides, but their structures are not stable under harsh acidic conditions, which is the usual condition for highly efficient HER.
The boron and nitrogen co-doped carbon nanomaterials (BCN) have recently gained much interest for their rich ternary system and potential electrochemical applications. Previous research generally required the addition of metal-based catalysts. In the year 2016, Zou’s group developed a facile catalyst-and-template-free strategy for easy fabrication and control of BCN nanomorphologies (J. Mater. Chem. A, 2016, 4, 16469-16475). By tuning the molecular weights of the polyethylene glycol carbon sources, BCN nanomorphologies from nanotubes to rolled graphene tubes were acquired, among which the B,N-doped graphene nanotubes showed the best electrochemical catalytic performance. The good conductivity and high intrinsic activities of the BCN nanotubes have granted them potential as electrochemical substrates for encapsulation of active metal species.
To further improve the electron transport and valid mass diffusion path for HER, Ruqiang Zou group applied this concept by using BCN nanotubes to confine MOFs derived CoP (CoP@BCN). The CoP@BCN nanotubes electrocatalysts have shown very low overpotential of 87, 215, and 122 mV at a current density of −10 mA cm−2 mV in acidic, basic, and buffer solution, respectively, and outstanding electrochemical stability. It was observed that H2 gas was solely produced in water electrolysis in acidic, buffer, and base solution with Faradaic efficiencies of 99.5%, 88.5%, and 76.7%, respectively.
Furthermore, in large cyclability, the outer wall of CoP@BCN nanotubes protected the encapsulated CoP nanoparticles from agglomeration and after a long time the structure remained almost unchanged in strong acidic conditions. The CoP@BCN exhibited best performance than most of the non-precious earth abundant catalysts performance and is expected to replace the precious metal catalysts. This unique synthetic strategy and competitive performance allow facile preparation of advanced CoP@BCN HER catalysts that may be readily integrated at large-scale water splitting devices.
Schematic illustration of construction of CoP@BCN nanostructures.
The Project was mainly completed by PhD student, Hassina Tabassum. The corresponding author was Professor Ruqiang Zou from the Department of Materials Science and Engineering, College of Engineering at Peking University.
This work was financially supported by the National Natural Science Foundation of China (Nos. 51322205 and 21371014) and National Program for Support of Top-notch Young Professionals, and Beijing Municipal Science and Technology Commission Program (Z151100000915074).