Plasma-Assisted Synthesis of Metal Nitrides for an Efficient Platinum-Group-Metal-Free Anion-Exchange-Membrane Fuel Cell

Abstract

In comparison to the well-developed proton-exchangemembrane fuel cells, anion-exchange-membrane fuel cells (AEMFCs) permit adoption of platinum-group-metal (PGM)-free catalysts due to the alkaline environment, giving a substantial cost reduction. However, previous AEMFCs have generally shown unsatisfactory performances due to the lack of effective PGM-free catalysts that can endure harsh fuel cell conditions. Here we report a plasma-assisted synthesis of highquality nickel nitride (Ni 3 N) and zirconium nitride (ZrN) employing dinitrogen as the nitrogen resource, exhibiting exceptional catalytic performances toward hydrogen oxidation and oxygen reduction in an alkaline enviroment, respectively. A PGM-free AEMFC assembled by using Ni 3 N as the anode and ZrN as the cathode delivers power densities of 256 mW cm −2 under an H 2 −O 2 condition and 151 mW cm −2 under an H 2 −air condition. Furthermore, the fuel cell shows no evidence of degradation after 25 h of operation. This work creates opportunities for developing high-performance and durable AEMFCs based on metal nitrides.

Nickel-Based Anode Catalysts for Efficient and Affordable Anion-Exchange Membrane Fuel Cells

“…Furthermore, reacting Ni with the nonmetallic N element to form Ni 3 N was also seen to boost HOR activity substantially, which shows a very small half-wave potential of 9.4 mV, comparing favorably to 14.0 mV measured on the MoNi 4 catalyst. 3 Together, the above results suggest vast possibilities for nontrivial HOR performances based on Ni through advisible catalyst design. The exchange current density (j 0 ) and kinetic current density (j k ) of various Ni-based catalysts are compared in Figure 4b.…”

“…Given the unique characteristics such as high electrical conductivity, high electrochemical stability, and good corrosion resistance, we were interested in metal nitrides and observed remarkable alkaline HOR and ORR activities over Ni 3 N and ZrN, respectively. 3 An H 2 −O 2 AEMFC assembled with Ni 3 N as the anode and ZrN as the cathode generates 148 mA cm −2 at 0.6 V and a peak power density of 256 mW cm −2 (Figure 7c). Switching to the H 2 −air condition, this device also delivers a peak power density of 151 mW cm −2 .…”

“…Unfortunately, when operating with air in an automobile, KOH solution in AFCs will react with CO 2 to form carbonates whose precipitation can block the porous electrode and reduce the ionic conductivity of an electrolyte . Although AEMFCs can mitigate this issue, Ni with sluggish HOR reactivity cannot work efficiently in AEMFCs due to the very low OH – concentration (∼0.1 M). , To improve HOR performance, substantial efforts have been made toward catalyst discovery based on the Ni element over the past 68 years (Figure b), which have led to several effective improvement strategies such as alloying, ,,,,− Ni nitridation, ,,− alloy amorphization, and others − (Figure c).…”

“…Using a similar ammonia annealing method, Hu’s group grew Ni 3 N nanoparticles on carbon and observed improved HOR activity and delayed surface oxidation, which they ascribed to a downshift of the d band from Ni to Ni 3 N, resulting in weakened adsorption of H and O species . In the search for a greener synthesis of metal nitrides, we developed very recently a plasma-assisted method that employs N 2 as a nitrogen resource, which allows access to the scalable production of the Ni 3 N catalyst (Figure e) . The resultant Ni 3 N shows very high quality, which not only displays outstanding HOR activity and stability on the rotating disk electrode (RDE) but also more intriguingly performs well in realistic fuel cells.…”

“…3,40,41 and Ni 3 N/C40 ), and alloy amorphization to form metallic glass (MG) (e.g., Ni 52 Mo 13 Nb 35 MG 2 ). Through sophisticated catalyst design, the electronic structure of Ni can be rationally tuned to control the surface-binding energetics of critical HOR intermediates, enhancing the HOR activity.…”