Solid polymer electrolyte electrochemical energy conversion devices that operate under highly alkaline conditions afford faster reaction kinetics and the deployment of inexpensive electrocatalysts compared with their acidic counterparts. The hydroxide anion exchange polymer is a key component of any solid polymer electrolyte device that operates under alkaline conditions. However, durable hydroxide-conducting polymer electrolytes in highly caustic media have proved elusive, because polymers bearing cations are inherently unstable under highly caustic conditions. Here we report a systematic investigation of novel arylimidazolium and bis-arylimidazolium compounds that lead to the rationale design of robust, sterically protected poly(arylimidazolium) hydroxide anion exchange polymers that possess a combination of high ion-exchange capacity and exceptional stability.

High performance benzyltrimethylammonium-type alkaline anion-exchange membranes (AEM), for application in electrochemical devices such as anion-exchange membrane fuel cells (AEMFC), were prepared by the radiation grafting (RG) of vinylbenzyl chloride (VBC) onto 25 μm thick poly(ethylene-co-tetrafluoroethylene) (ETFE) films followed by amination with trimethylamine. Reductions in electron-beam absorbed dose and amount of expensive, potentially hazardous VBC were achieved by using water as a diluent (reduced to 30 – 40 kGy absorbed dose and 5%vol VBC) instead of the prior-art method that used organic propan-2-ol diluent (required 70 kGy dose and 20%vol VBC monomer). Furthermore, the water from the aqueous grafting mixture was easily separated from residual monomer (after cooling) and was reused for a further grafting reaction: the resulting AEM exhibited an ion-exchange capacity of 2.1 mmol g-1 (cf. 2.1 mmol g-1 for the AEM made using fresh grafting mixture). The lower irradiation doses resulted in mechanically stronger RG-AEMs compared to the reference RG-AEM synthesised using the prior-art method. A further positive off-shoot of the optimisation process was the discovery that using water as a diluent resulted in an enhanced (i.e. more uniform) distribution of VBC grafts as proven by Raman microscopy and corroborated using EDX analysis: this led to enhancement in the Cl- anion-conductivities (up to 68 mS cm-1 at 80°C for the optimised fully hydrated RG-AEMs vs. 48 mS cm-1 for the prior-art RG-AEM reference). A down-selected RG-AEM of ion-exchange capacity = 2.0 mmol g-1, that was synthesised using the new greener protocol with 30 kGy electron-beam absorbed dose, led to an exceptional beginning-of-life H2/O2 AEMFC peak power density of 1.16 W cm−2 at 60°C in a benchmark test using industrial standard Pt-based electrocatalysts and unpressurised gas supplies: this was higher than the 0.91 W cm-1 obtained with the reference RG-AEM (IEC = 1.8 mmol g-1) synthesised using the prior-art protocol

Efficient and durable nonprecious metal electrocatalysts for the oxygen reduction (ORR) are highly desirable for several electrochemical devices, including anion exchange membrane fuel cells (AEMFCs). Here, a 2D planar electrocatalyst with CoO x embedded in nitrogen‐doped graphitic carbon (N‐C‐CoO x ) was created through the direct pyrolysis of a metal–organic complex with a NaCl template. The N‐C‐CoO x catalyst showed high ORR activity, indicated by excellent half‐wave (0.84 V vs. RHE) and onset (1.01 V vs. RHE) potentials. This high intrinsic activity was also observed in operating AEMFCs where the kinetic current was 100 mA cm −2 at 0.85 V. When paired with a radiation‐grafted ETFE powder ionomer, the N‐C‐CoO x AEMFC cathode was able to achieve extremely high peak power density (1.05 W cm −2 ) and mass transport limited current (3 A cm −2 ) for a precious metal free electrode. The N‐C‐CoO x cathode also showed good stability over 100 hours of operation with a voltage decay of only 15 % at 600 mA cm −2 under H 2 /air (CO 2 ‐free) reacting gas feeds. The N‐C‐CoO x cathode catalyst was also paired with a very low loading PtRu/C anode catalyst, to create AEMFCs with a total PGM loading of only 0.10 mg Pt‐Ru cm −2 capable of achieving 7.4 W mg −1 PGM as well as supporting a current of 0.7 A cm −2 at 0.6 V with H 2 /air (CO 2 free)—creating a cell that was able to meet the 2019 U.S. Department of Energy initial performance target of 0.6 V at 0.6 A cm −2 under H 2 /air with a PGM loading <0.125 mg cm −2 with AEMFCs for the first time.

Efficient and durable nonprecious metal electrocatalysts for the oxygen reduction (ORR) are highly desirable for several electrochemical devices,i ncluding anion exchange membrane fuel cells (AEMFCs). Here,a2D planar electrocatalyst with CoO x embedded in nitrogen-doped graphitic carbon (N-C-CoO x )was created through the direct pyrolysis of am etal-organic complex with aN aCl template.T he N-C-CoO x catalyst showed high ORR activity,indicated by excellent half-wave (0.84 Vv s. RHE) and onset (1.01 Vv s. RHE) potentials.T his high intrinsic activity was also observed in operating AEMFCs where the kinetic current was 100 mA cm À2 at 0.85 V. When paired with ar adiation-grafted ETFE powder ionomer,t he N-C-CoO x AEMFC cathode was able to achieve extremely high peak power density (1.05 Wcm À2 )a nd mass transport limited current (3 Acm À2 ) for ap recious metal free electrode.T he N-C-CoO x cathode also showed good stability over 100 hours of operation with av oltage decayo fo nly 15 %a t6 00 mA cm À2 under H 2 /air (CO 2 -free) reacting gas feeds.The N-C-CoO x cathode catalyst was also paired with avery low loading PtRu/C anode catalyst, to create AEMFCs with atotal PGM loading of only 0.10 mg Pt-Ru cm À2 capable of achieving 7.4 Wmg À1 PGM as well as supporting ac urrent of 0.7 Acm À2 at 0.6 Vw ith H 2 /air (CO 2 free)creating acell that was able to meet the 2019 U.S. Department of Energy initial performance target of 0.6 Va t0 .6 Acm À2 under H 2 /air with aP GM loading < 0.125 mg cm À2 with AEMFCs for the first time.