Alkaline fuel cells and electrolyzers are of interest because they have potential advantages over their acid counterparts. High-conductivity anion conducting membranes were analyzed and used in alkaline hydrogen/oxygen fuel cells. The membranes were composed of reinforced block copolymers of poly(norbornenes) with pendant quaternary ammonium head-groups. It was found that membranes with light cross-linking provided excellent mechanical stability and allowed very high ion exchange capacity polymers to be used without penalty of excessive water uptake and swelling. The optimum membrane and fuel cell operating conditions were able to achieve a peak power density of 3.4 W/cm² using hydrogen and oxygen. The performance increase was greater than expected from minimizing ohmic losses. Mechanical deformations within the membrane due to excess water uptake can disrupt full cell operation. Cells were also run for over 500 h under load with no change in the membrane resistance and minimal loss of operating voltage.

High ionic conductivity membranes can be used to minimize ohmic losses in electrochemical devices such as fuel cells, flow batteries, and electrolyzers. Very high hydroxide conductivity was achieved through the synthesis of a norbornene-based tetrablock copolymer with an ion-exchange capacity of 3.88 meq/g. The membranes were cast with a thin polymer reinforcement layer and lightly cross-linked with N,N,N′,N′-tetramethyl-1,6-hexanediamine. The norbornene polymer had a hydroxide conductivity of 212 mS/cm at 80°C. Light cross-linking helped to control the water uptake and provide mechanical stability while balancing the bound (i.e. waters of hydration) vs. free water in the films. The films showed excellent chemical stability with <1.5% conductivity loss after soaking in 1 M NaOH for 1000 h at 80°C. The aged films were analyzed by FT-IR before and after aging to confirm their chemical stability. A H₂/O₂ alkaline polymer electrolyte fuel cell was fabricated and was able to achieve a peak power density of 3.5 W/cm² with a maximum current density of 9.7 A/cm² at 0.15 V at 80°C. The exceptionally high current and power densities were achieved by balancing and optimizing water removal and transport from the hydrogen negative electrode to the oxygen positive electrode. High water transport and thinness are critical aspects of the membrane in extending the power and current density of the cells to new record values.

It has previously been shown that phase-separated block copolymers with non-ion conducting (hydrophobic) blocks and ion conducting (hydrophilic) blocks can form efficient ion conducting channels with high ionic mobility and conductivity. Block copolymers can provide a means for phase segregation and ion channel formation while homopolymers and random copolymers have been shown to have lower ion mobility. In this study, the properties of poly(norbornene) based anion exchange membranes (AEMs) comprising homopolymers, block copolymers, and random copolymers with high ion-exchange capacity (IEC) (3.48–4.55 meq. g⁻¹) have been investigated and compared. The polymers were cross-linked with N,N,N′,N′-tetramethyl-1,6-hexanediamine before casting the membranes to avoid excessive water swelling due to high water uptake. It was shown that high ionic conductivity can be achieved in both random copolymers and homopolymers even in the absence of microphase-separated structures. For example, the conductivity of a random copolymer was 194 mS cm⁻¹ at 80 °C, which was comparable to the block copolymer, 201 mS cm⁻¹ at 80 °C. The H₂/O₂ fuel cell performance of random copolymer composite membranes showed a peak power density of 3.05 W cm⁻² and peak current density of 7.85 A cm⁻² at 80 °C compared to block copolymer membranes (peak power density of 3.21 W cm⁻² and peak current density of 8.27 A cm⁻² at 80 °C). It is more critical that high water transport be achieved in AEMs than achieving a phase-segregated morphology. Finally, the homopolymer, block copolymer, and random copolymer membranes showed <1.35% degradation after aging in 1 M NaOH at 80 °C for 1000 h.