Gas management in battery systems remains a critical challenge, particularly concerning the accumulation of gaseous byproducts during operation. Porous materials such as metal-organic frameworks (MOFs) and porous carbons have emerged as promising candidates for in-cell gas capture due to their high surface areas, tunable pore structures, and selective adsorption properties. These materials function through physisorption mechanisms, where gas molecules are trapped within their porous networks without chemical bonding, allowing for reversible capture and release.

Metal-organic frameworks are crystalline materials composed of metal ions or clusters linked by organic ligands, forming highly ordered porous structures. Their porosity can be precisely engineered to target specific gases, such as oxygen, carbon dioxide, or hydrogen, which may evolve during battery cycling. The physisorption process in MOFs relies on van der Waals interactions, where gas molecules adhere to the internal surfaces of the pores. The adsorption capacity is influenced by factors such as pore size, surface chemistry, and operating conditions like temperature and pressure. For instance, MOFs with open metal sites or functionalized ligands exhibit enhanced affinity for polar gas molecules, improving selectivity.

Porous carbons, including activated carbon, carbon nanotubes, and graphene-derived frameworks, also demonstrate excellent gas adsorption properties. Their disordered yet highly interconnected pore networks provide ample sites for gas entrapment. Unlike MOFs, carbons typically lack the same degree of structural precision but compensate with robustness, chemical stability, and cost-effectiveness. The physisorption mechanism in porous carbons involves gas molecules occupying micropores (less than 2 nm) and mesopores (2-50 nm), with the highest adsorption occurring in micropores due to stronger confinement effects. Surface modifications, such as nitrogen doping, can further enhance gas uptake by introducing polar sites that interact more strongly with gas molecules.

A critical consideration for in-cell gas capture is the impact of capacity degradation over time. Repeated adsorption-desorption cycles can lead to structural changes in the porous material, reducing its effectiveness. For MOFs, framework collapse or ligand decomposition may occur under prolonged exposure to battery electrolytes or elevated temperatures. Certain MOFs are susceptible to hydrolysis, particularly those with coordinatively unsaturated metal centers, which can degrade in the presence of moisture or acidic byproducts. Additionally, pore blocking by electrolyte decomposition products can diminish gas accessibility, lowering adsorption capacity.

Porous carbons generally exhibit better stability than MOFs in harsh electrochemical environments, but they are not immune to degradation. Oxidation of carbon surfaces can occur at high voltages, altering pore structure and reducing gas uptake. Furthermore, the deposition of solid electrolyte interphase (SEI) components or other insoluble species may clog pores over time. The mechanical integrity of porous carbons can also degrade under prolonged cycling, leading to particle fragmentation and loss of active adsorption sites.

Comparative studies between MOFs and porous carbons reveal trade-offs in performance and durability. MOFs often achieve higher initial gas uptake due to their ultrahigh surface areas, which can exceed 7000 m²/g in some cases. However, their long-term stability in battery systems remains a concern. Porous carbons, while typically offering lower initial capacities (ranging from 500 to 3000 m²/g), demonstrate better resilience under operational stresses. Hybrid approaches, such as MOF-carbon composites, have been explored to combine the advantages of both materials, though challenges in interfacial compatibility and scalable synthesis persist.

The effectiveness of porous materials for gas capture is also influenced by battery design and operating conditions. In closed-cell configurations, where gas pressure may build up, the adsorption kinetics of the material become crucial. Materials with rapid gas uptake and release rates are preferred to prevent pressure-induced cell failure. Temperature fluctuations during cycling can further affect adsorption performance, as physisorption is inherently temperature-dependent. Elevated temperatures reduce gas uptake due to decreased adsorption enthalpies, while lower temperatures enhance it but may slow kinetics.

Efforts to mitigate capacity degradation focus on material optimization and protective strategies. For MOFs, hydrophobic coatings or post-synthetic modifications can improve moisture resistance. Selecting thermally stable ligands and robust metal nodes enhances structural integrity. In porous carbons, graphitization or surface passivation reduces oxidative damage. Pre-treating materials with gas-selective functional groups can also improve longevity by minimizing competitive adsorption from unwanted species.

Integration of porous gas capture materials into battery systems requires careful consideration of placement and compatibility. Positioning adsorbents near gas evolution hotspots, such as electrodes or separator interfaces, maximizes efficiency. However, direct contact with reactive components must be avoided to prevent unwanted side reactions. Thin-film coatings or embedded porous layers within separators have been proposed as practical solutions, though scalability remains a hurdle.

Future advancements in porous materials for in-cell gas capture will likely focus on multifunctional designs that combine gas adsorption with other beneficial properties, such as mechanical reinforcement or electrolyte stabilization. Computational modeling aids in predicting gas-material interactions and degradation pathways, guiding the development of next-generation adsorbents. Experimental validation under realistic battery conditions remains essential to bridge the gap between laboratory-scale results and industrial implementation.

In summary, porous materials like MOFs and carbons offer viable solutions for mitigating gas-related issues in batteries through physisorption. While MOFs provide superior tunability and initial performance, their stability limitations necessitate further refinement. Porous carbons present a more robust alternative, albeit with trade-offs in capacity. Addressing degradation mechanisms through material engineering and system integration will be key to realizing their full potential in enhancing battery safety and longevity.