The generation of renewable electricity is variable, leading to periodic oversupply. Excess power can be converted to H2via water electrolysis, but the conversion cost is currently too high. One way to decrease the cost of electrolysis is to increase the maximum productivity of electrolyzers. This study investigates how nano‐ and microstructured porous electrodes can improve the productivity of H2generation in a zero‐gap, flow‐through alkaline water electrolyzer. Three nickel electrodes—foam, microfiber felt, and nanowire felt—are studied to examine the tradeoff between surface area and pore structure on the performance of alkaline electrolyzers. Although the nanowire felt with the highest surface area initially provides the highest performance, this performance quickly decreases as gas bubbles are trapped within the electrode. The open structure of the foam facilitates bubble removal, but its small surface area limits its maximum performance. The microfiber felt exhibits the best performance because it balances high surface area with the ability to remove bubbles. The microfiber felt maintains a maximum current density of 25 000 mA cm−2over 100 h without degradation, which corresponds to a hydrogen production rate 12.5‐ and 50‐times greater than conventional proton‐exchange membrane and alkaline electrolyzers, respectively.
Recent advances in fundamental performance limits for power quantities based on Lagrange duality are proving to be a powerful theoretical tool for understanding electromagnetic wave phenomena. To date, however, in any approach seeking to enforce a high degree of physical reality, the linearity of the wave equation plays a critical role. In this manuscript, we generalize the current quadratically constrained quadratic program framework for evaluating linear photonics limits to incorporate nonlinear processes under the undepleted pump approximation. Via the exemplary objective of enhancing second harmonic generation in a (free-form) wavelength-scale structure, we illustrate a model constraint scheme that can be used in conjunction with standard convex relaxations to bound performance in the presence of nonlinear dynamics. Representative bounds are found to anticipate features observed in optimized structures discovered via computational inverse design. The formulation can be straightforwardly modified to treat other frequency-conversion processes, including Raman scattering and four-wave mixing.
more » « less- NSF-PAR ID:
- 10479336
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 31
- Issue:
- 26
- ISSN:
- 1094-4087; OPEXFF
- Format(s):
- Medium: X Size: Article No. 44212
- Size(s):
- ["Article No. 44212"]
- Sponsoring Org:
- National Science Foundation
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