Commercially used platinum/carbon (Pt/C) catalysts are susceptible to ammonia poisoning in hydrogen fuel cells, resulting in reduced performance. To make matters worse, the hydrogen oxidation reaction on platinum-based catalysts has slower kinetics in alkaline membrane fuel cells, interacting with ammonia poisoning to accelerate performance degradation. Therefore, there is an urgent need for an anode catalyst with high activity and high resistance to ammonia toxicity in the application of AEMFC. Therefore, there is an urgent need for an anode catalyst with high activity and high resistance to ammonia toxicity in the application of AEMFC.
Recently, a research team led by Professor Gao Jianming of the Chinese Academy of Sciences at the University of Science and Technology of China (USTC) developed a nickel (Ni) -based anode catalyst for ammonia toxicity resistant anode exchange membrane fuel cell (AEMFC). The work was published in the Journal of the American Chemical Society.
Hydrogen fuel cell, as a pollution-free power source with high specific energy, plays an important role in the current energy industry. However, commercially used platinum/carbon (Pt/C) catalysts are susceptible to ammonia poisoning in hydrogen fuel cells, resulting in performance degradation. To make matters worse, the hydrogen oxidation reaction on platinum-based catalysts has slower kinetics in alkaline membrane fuel cells, interacting with ammonia poisoning to accelerate performance degradation. Therefore, there is an urgent need for an anode catalyst with high activity and high resistance to ammonia toxicity in the application of AEMFC.
The researchers concluded that the enrichment of electrons around the nickel site could repel the lone pair donation of ammonia (NH3 ), while the inclusion of metal elements with less electronegativity than nickel could provide electrons to obtain electron-rich States. By doping chromium (Cr) into the highly efficient hydrogen oxidation catalyst molybdenum-nickel alloy (MoNi4), the team not only obtained the electron-rich state of nickel and inhibited the electron supply of σN-H → dmetal, but also shifted the d-band center down and blocked the reverse electron supply of d → σ * N-H, both of which greatly weakened the adsorption of ammonia.
Rotating rotary electrode (RDE) tests showed that the Cr-MoNi4 catalyst exhibited no significant activity decay in the presence of 2 ppm NH3 for 10,000 cycles, while the conventional Pt/C catalyst exhibited severe activity decay under such conditions. In an alkaline membrane fuel cell actually assembled with Cr-MoNi4 as the anode, it can maintain 95% of the initial peak power density in the presence of 10 ppm NH3 , compared to 65% for the Pt/C catalyst.
The results show that the chromium modifier creates an electron-rich state, which effectively suppresses the σN-H → d supply and shifts down the d-band center. Less d-band filling also limits the d electron supply to the σ * N-H orbital of ammonia, thus synergistically weakening the binding of NH3 . In conclusion, Cr-MoNi4 can be used as a highly efficient, highly resistant to ammonia toxicity, and cost-effective negative HOR catalyst for AEMFC anodes.
The rotating electrode test shows that in the presence of 2 ppm NH3 , there is no obvious change in the composition and structure of Cr-MoNi4 after 10000 cycles. And that performance of the platinum-carbon catalyst is severely degrade. If placed in an AEMFC, devices assembled using Cr-MoNi4 can maintain 95% of the initial peak power density in the presence of 10 ppm NH3 .
Attenuated-total-reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements show that the chromium-free MoNi4 and commercial Pt/C catalysts exhibit different ammonia adsorption behaviors at different potentials. However, the chromium-modified catalyst has no NH3 adsorption peak. Electron energy loss spectroscopy (EELS) and electron paramagnetic resonance (EPR) measurements also show that the addition of chromium increases the occupancy of the d-band States. Professor
Gao's team has been working on the development and application of non-noble metal electrocatalysts for AEMFCs. These findings will drive future research on platinum-group metal (PGM) -free catalysts in hydrogen fuel cells against impurity gas poisoning.
According to the researchers, this research work will further promote the practical application of alkaline membrane fuel cell technology.
浙公网安备33010802003254号