Mn-modified nitrogen-doped Pt-based electrocatalyst for efficient oxygen reduction in aluminum-air batteries

In this study,a Mn-modified Pt-based catalyst loaded on nitrogen-doped Ketjen black(Mn-Pt/NKB)is prepared using a simple ethylene glycol reduction method.The size of Pt nanoparticles(NPs)is effectively controlled by doping with Mn and N.With the smallest average particle size of 1.7 nm,Mn-Pt/NKB demonstrates half-wave potentials of 0.890 and 0.688 V in the alkaline and neutral electrolytes,respectively,which are superior to those of commercial platinum on activated carbon(Pt/C).When applied as an air cathode in aluminum-air battery,it exhibits ultra-high power densities of 190(alkaline)and 26.2 mW·cm^(−2)(neutral).Moreover,the voltage remains stable after 5 h of discharge.The practical application performance of the Mn-Pt/NKB catalyst in an aluminum-air battery is better than that of commercial Pt/C.Furthermore,the oxygen reduction reaction(ORR)mechanism on surfaces with different particle sizes is analyzed using density functional theory.Oxygen cracking is the major pathway on the surface of the small particles with lower energy consumption of 0.5 eV,while water molecule cleavage is the major pathway on the surface of the large particles with higher energy consumption of 0.97 eV.The lower energy consumption of the oxygen cracking pathway further confirms the ORR mechanism for higher activity on small-sized surfaces.This study provides a direction for the rational design of Pt-based catalysts for ORR and sheds light on the commercial development of aluminum-air batteries.

Current challenge and perspective of PGM-free cathode catalysts for PEM fuel cells

To significantly reduce the cost of proton exchange membrane fuel cells, platinum-group metal （PGM）-free cathode catalysts are highly desirable. Current M-N-C （M： Fe, Co or Mn） catalysts are considered the most promising due to their encouraging performance. The challenge thus has been their stability under acidic conditions, which has hindered their use for any practical applications. In this review, based on the author＇s research experience in the field for more than 10 years, current challenges and possible solutions to overcome these problems were discussed. The current Edisonian approach （i.e., trial and error） to developing PGM-free catalysts has been ineffective in achieving revolutionary breakthroughs. Novel synthesis techniques based on a more methodolo- gical approach will enable atomic control and allow us to achieve optimal electronic and geometric structures for active sites uniformly dispersed within the 3D architec- tures. Structural and chemical controlled precursors such as metal-organic frameworks are highly desirable for making catalysts with an increased density of active sites and strengthening local bonding structures among N, C and metals. Advanced electrochemical and physical characterization, such as electron microscopy and X-ray absorption spectroscopy should be combined with first principle density functional theory （DFT） calculations to fully elucidate the active site structures.