For high rate water electrolysers, minimising Ohmic losses through efficient gas bubble evacuation away from the active electrode is as important as minimising activation losses by improving the electrode’s electrocatalytic properties. In this work, by a combined experimental and computational fluid dynamics (CFD) approach, we identify the topological parameters of flow-engineered 3-D electrodes that direct their performance towards enhanced bubble evacuation. In particular, we show that integrating Ni-based foam electrodes into a laterally-graded bi-layer zero-gap cell configuration allows for alkaline water electrolysis to become Proton Exchange Membrane (PEM)-like, even when keeping a state-of-the-art Zirfon diaphragm. Detailed CFD simulations, explicitly taking into account the entire 3-D electrode and cell topology, show that under a forced uniform upstream electrolyte flow, such a graded structure induces a high lateral velocity component in the direction normal to and away from the diaphragm. This work is therefore an invitation to start considering PEM-like cell designs for alkaline water electrolysis as well, in particular the use of square or rectangular electrodes in flow-through type electrochemical cells.

A new membrane fabrication process is presented, in which PBI is cast from a phosphoric acid-based solution and transformed into a KOH doped membrane by immersion in KOH solution. At room temperature, such membranes show a remarkably high conductivity of 300 mS cm⁻¹ in 25 wt% KOH solution, 3 times higher than that of conventional PBI membranes cast from DMAc. While swelling of PBI in KOH solution is highly anisotropic, the phosphoric acid-cast membrane shrinks isotropically when immersed in KOH solution, indicating that the ordered, presumably lamellar structures, which are suspected to hinder transfer of ions through the membrane, are transferred into a gel-state. This is further supported by WAXS analysis. DFT calculations suggest that the broad signal in WAXS is related to the distance between hydrogen bonded imidazolides. The soft nature of the KOH doped PBI was mitigated by reinforcement with porous supports. By using a PTFE support, the tensile strength increased from 2 to 32 MPa, and the Young's modulus from 19 to 80 MPa. Immersion in 25 wt% KOH at 80 °C indicated high stability. In the electrolyzer, a conventional PBI membrane failed within 200 hours. In contrast to this, a PTFE-supported separator reached 1.8 A cm⁻² at 1.8 V and was operated for 1000 hours without failure, which is the longest operation time for ion-solvating membranes to date.

Anion exchange membrane water electrolyzers (AEMWEs) offer a cost‐effective technology for producing green hydrogen. Here, an AEMWE with atmospheric plasma spray non‐precious metal electrodes was tested in 0.1 to 1.0 M KOH solution, correlating performance with KOH concentration systematically. The highest cell performance was achieved at 1.0 M KOH (ca. 0.4 A cm⁻² at 1.80 V), which was close to a traditional alkaline electrolysis cell with ≈6.0 M KOH. The cell exhibited 0.13 V improvement in the performance in 0.30 M KOH compared with 0.10 M KOH at 0.5 A cm⁻². However, this improvement becomes more limited when further increasing the KOH concentration. Electrochemical impedance and numerical simulation results show that the ohmic resistance from the membrane was the most notable limiting factor to operate in low KOH concentration and the most sensitive to the changes in KOH concentration at 0.5 A cm⁻². It is suggested that the effect of activation loss is more dominant at lower current densities; however, the ohmic loss is the most limiting factor at higher current densities, which is a current range of interest for industrial applications.

Rationally designed free-standing and binder-free Raney-type nickel–molybdenum (Ni–Mo) electrodes produced via atmospheric plasma spraying (APS) are developed by correlating APS process parameters with the microstructure of electrodes and their electrochemical performance in alkaline media. The results revealed that the electrode morphology and elemental composition are highly affected by the plasma parameters during the electrode fabrication. It is found that increasing plasma gas flow rate and input plasma power resulted in higher in-flight particle velocities and shorter dwell time, which in result delivered electrodes with much finer structure exhibiting homogeneous distribution of phases, larger quantity of micro pores and suitable content of Ni and Mo. Tafel slope of electrodes decreased with increasing the in-flight particles velocities from 71 to 33 mV dec⁻¹in 30 wt.% KOH. However, beyond a critical threshold in-flight velocity and temperature of particles, electrodes started to exhibit larger globular pores and consequently reduced catalytic performance and higher Tafel slop of 36 mV dec⁻¹in 30 wt.% KOH. Despite slightly lower electrochemical performance, the electrodes produced with highest plasma gas flow and energy showed most inter-particle bonded structure as well as highest stability with no measurable degradation over 47 days in operation as HER electrode in 30 wt.% KOH. The Raney-type Ni–Mo electrode fabricated at highest plasma gas flow rate and input plasma power has been tested as HER electrode in alkaline water electrolyzer, which delivered high current densities of 0.72 and 2 A cm⁻²at 1.8 and 2.2 V, respectively, representing a novel prime example of HER electrode, which can synergistically catalyze the HER in alkaline electrolyzer. This study shows that sluggish alkaline HER can be circumvented by rational electrode composition and interface engineering.

Ion solvating membranes based on polybenzimidazole (PBI) are alternatives to diaphragms in alkaline water electrolysers but can typically only operate with electrolyte concentrations of 15–30 wt% KOH. Sulfonation of the membrane broadens the operational range to 0.1 wt%–30 wt%; however, the swelling of sulfonated para -PBI means that crosslinkers are needed, complicating membrane fabrication and decreasing alkaline stability. Here we report a non-crosslinked PBI membrane with a 50% degree of sulfonation that shows a high room temperature conductivity in 1 M KOH of 135 mS cm ⁻¹ . We did not observe degradation in a 6-month alkaline stability test at 80 °C. Using this membrane in an anion-exchange membrane water electrolyser, we report a current density of 4.8 A cm ⁻² at 2 V (3 M KOH at 80 °C; Pt and NiFe electrode catalysts); the H ₂ crossover to the O ₂ side remained 1,000 h without failure.

Charge-transfer process (CTP) and mass-transfer process (MTP) are essential in water electrolysis. The engineered core@shell nanoarrays-based anode can significantly improve not only CTP but also MTP in AWE cell.