Each step up this curve buys a better kWh/kg with a pricier stack. Which design gives the cheapest hydrogen depends on what your power costs and how many hours the stack runs: cheap solar at low utilization pays for almost none of the tricks, while expensive power run 24/7 over a long life pays for nearly all of them, up to a $2,000/kW noble-metal stack.
Design steps and costs are read off the post's "Electrolyzer Design Trades" chart (Casey Handmer, 2024). Hydrogen cost = kWh/kg × (power price + capex ÷ hours run), with hours run = years × 8,760 × utilization.