Magnesium batteries offer a promising alternative to lithium-ion systems, but suitable electrodes remain limited. Covalent organic frameworks (COFs) are attractive candidates due to their structural tunability and open channels for ion transport. We report a pyrene- 4,5,9,10-tetraone COF composite with carbon nanotubes as a Mg electrode, delivering 70 mAh g at 200 mA g and operating at 1.3 V. Raman spectroscopy confirms carbonyl-centered redox on pyrene tetraone, supporting a Mg-driven carbonyl reduction. Compared with Li, only partial carbonyl utilization occurs, attributed to steric and electrostatic constraints of divalent Mg. This incomplete conversion to magnesium-enolate inspires future work toward structural optimization.

In this work, we report the synthesis and structural characterization of the beryllium-based metal-organic framework of general formula [BeO-(BDC-NH)(OAc)] ( ), designed for combined physical and chemical hydrogen storage applications. The material was extensively characterized through a plethora of solid-state techniques (including less conventional Be NMR-MAS spectroscopy). Structural analysis by X-ray powder diffraction confirmed the formation of a crystalline porous framework of topology isostructural to MOF-5 and to MOF-5-(Be), while thermogravimetric studies revealed remarkable thermal stability up to 830 K. Nitrogen adsorption measurements demonstrated a high specific surface area (2264 m/g after removal of residual acetic acid), confirming the accessible porosity of the material. Hydrogen adsorption experiments (physical hydrogen storage) performed at cryogenic temperatures showed fast, fully reversible physisorption with a gravimetric H density of 8.0 wt % H ( = 77 K, = 80 bar) and a H isosteric heat of adsorption of 2.7 kJ/mol (at 0.1 wt % H coverage), consistent with weak, noncovalent interactions between the hydrogen molecules and the framework. To enable chemical hydrogen storage, ammonia borane (NH·BH, AB, 19.6 wt % H) was successfully impregnated into the MOF pores by suspending it on concentrated methanol solutions of AB. Solid-state multinuclear (B, N) NMR spectroscopy revealed the presence of several boron-containing species, indicating partial chemical transformations of ammonia borane within the framework triggered by the formation of an initial B-H···H-N dihydrogen bonding interaction with the amino dangling group on the MOF linker. B NMR quantification determined a maximum hydride loading of 2.1 AB molecules per formula unit. To our knowledge, this is the first example of a beryllium MOF able to host either physisorbed molecular hydrogen or chemically bound hydrogen in the form of BN-based lightweight inorganic hydrides, highlighting its potential as a multifunctional material for advanced hydrogen storage strategies.

Nanoscale transition metal phosphide systems hold significant technological potential due to their distinctive optoelectronic properties, high catalytic activity, superparamagnetism, and high diffusion coefficient of Na/Li ions. However, attempts to synthesize phase-pure FeP, a promising electrocatalyst, have utilized expensive and/or highly reactive phosphide precursors such as tri--octylphosphine (TOP), white phosphorus (P), tris-(trimethylsilyl)-phosphine (P-(TMS)), and tri--butylphosphine. These methods often require high temperatures and/or multistep reaction processes. Here, to address these limitations, we present a solution-based synthesis method to produce phase-pure FeP nanoparticles. In this synthesis, we react iron oxyhydroxide (β-FeOOH) as a cost-effective, environmentally friendly, and air-stable source of iron with tris-diethylaminophosphine P-(NEt) as a phosphorus source at 280 °C. The resulting FeP is formed in a porous nanorod morphology. The particles were characterized by TEM and XPS. Magnetic measurements of the phase-pure FeP nanoparticles indicate paramagnetic behavior, contrasting the antiferromagnetic behavior observed in bulk FeP. In addition to their unique magnetic properties, these porous FeP nanorods demonstrate promising HER performance, achieving an overpotential of 267 mV at a geometric current density of -10 mA cm in acidic media, with stable electrocatalytic activity maintained for up to 12 h at -50 mA cm. This study represents the first documented low-temperature, time-efficient, solution-based thermal decomposition method for synthesizing phase-pure FeP nanoparticles, using tris-(diethylamino)-phosphine P-(NEt) and iron oxyhydroxide (β-FeOOH) as sources of phosphorus and iron, respectively, at 280 °C.

Electrocatalytic reduction of CO to multicarbon products represents a key target in the development of artificial (photo)-synthetic systems. Copper-based electrodes are uniquely suited for this purpose, yet achieving high selectivity toward C-C coupled products such as ethylene, over undesired byproducts like methane and hydrogen, remains a major challenge. Surface engineering has emerged as a powerful strategy to steer the selectivity of CO electroreduction toward ethylene. Here, we introduce a modular hybrid electrode architecture composed of copper nanowires (CuNWs) coated with a thin, functional organic shell formed via electroreduction of ethylene-bridged dipyridophenazine () dication derivatives. This core-shell architecture enables fine-tuning of the interfacial catalytic environment through rational molecular design. We demonstrate that subtle structural variations affecting the electronic distribution of the phenazine moiety have a profound effect on ethylene selectivity. Notably, electrodes incorporating electron-withdrawing groups achieved nearly a tenfold increase in Faradaic efficiency for ethylene relative to pristine CuNWs, whereas hydrophilic functionalities favored hydrogen production and suppressed C and C products. DFT calculations reveal how the substituents alter local electric fields and interfacial water binding, providing a molecular-level rationale for the observed trends. Ex situ characterization of core-shell electrodes further reveals that the polymeric coating stabilizes the Cu surface against corrosion and provides valuable insights into the structural reconstruction of CuNWs during the electrocatalytic process. This work not only advances the fundamental understanding of hybrid interface effects by providing a powerful and scalable approach for decoupling catalyst selectivity from the intrinsic properties of the metal surface but also offers a promising route toward efficient and industrially relevant carbon conversion technologies.

Lithium-sulfur (Li-S) batteries suffer from the dissolution of sulfur and polysulfide (PS) species in the electrolyte, leading to capacity loss, instability, and a shortened lifespan. While highly concentrated electrolytes have been explored to address this issue, the underlying mechanisms of S/PS dissolution and subsequent diffusion, particularly concerning the specific behavior of long- and short-chain PSs under varying states of charge (SOC), remain poorly understood. We here employ Raman spectroscopy to semiquantitatively monitor PS solubility and migration across a wide range of LiTFSI concentrations in DME:DOL (1:1, v/v). We find that both PS dianions (S ) and trisulfur radicals (S ) decrease at the lithium anode with increasing electrolyte salt concentration (0.3-7.0 m), indicating reduced solubility and slower transport. Notably, the concentration of S decreases more rapidly than that of its parent PS S , suggesting less favorable radical formation pathways in highly concentrated electrolytes, potentially due to Li-TFSI-PS adduct formation. These changes result from shifts in the local solvation structure at high salt concentration, thereby controlling the solubility, transport, and chemical pathways of polysulfides in the electrolyte. By providing the real-time dynamics of long- and short-chain PSs, this work advances the mechanistic understanding of PSs in order to provide valuable insight for further improvement of Li-S battery performance.

Viologen derivatives are widely used in the anolytes of aqueous organic redox flow batteries (AORFBs). However, their applications have been restricted to neutral pH systems due to their fast degradation in basic media via a dealkylation process driven by a nucleophilic attack of hydroxide. In this study, a family of viologen-based anolytes suitable for alkaline systems is introduced, demonstrating that properly designed viologens can also be used in alkaline conditions. A variety of -aryl viologens are prepared and characterized, showing that the dealkylation process is prevented by bonding an aryl group directly to the N-atom of the bipyridine core. Pairing for the anolyte and KFe-(CN) for the catholyte, a full alkaline AORFB having a nominal cell voltage at 0.98 V maintains stable capacity over 1400 continuous cycles with nearly 0.03%·h capacity decay, which is a very acceptable value for a viologen in an alkaline medium. Our results enable the broadening of the range of viable organic anolytes for alkaline AORFBs.

Potassium metal batteries (PMBs) are gaining attention as low-cost, sustainable, and high-energy storage. Their practical implementation, however, is impeded by instability of the potassium (K) metal anode, manifested as dendritic growth, large volume fluctuations, and fragile solid electrolyte interphases (SEIs), all of which accelerate capacity fading and safety risks. This review highlights recent advances in substrate design for stabilizing K metal anodes, categorized into five strategies: (i) three-dimensional host architectures, (ii) heteroatom doping and molecular grafting, (iii) inorganic nanoparticle incorporation, (iv) alloying seed engineering, and (v) substrate-regulated SEI formation via work function modulation. Mechanistic insights from experimental and theoretical studies are integrated with performance comparisons to evaluate trade-offs between deposition control, SEI stability, scalability, and cost. Key challenges for commercialization are outlined, including long-term cycling under practical conditions, integration with high-energy-density cathodes, and scalable fabrication. By advancing structural, chemical, and electronic design principles, PMBs can progress toward reliable, high-performance energy storage.

Selenium solar cells (SeSCs) are gaining renewed interest as wide band gap photovoltaic absorbers suitable for indoor energy harvesting and tandem applications. While significant progress has been made through extensive optimization of electron transport layers (ETLs), the role of hole transport layers (HTLs) has been comparatively less explored. In this work, we investigate the integration of inorganic transition metal oxides (TMOs), namely molybdenum oxide (MoO ), tungsten oxide (WO ), and vanadium oxide (VO ), as hole-selective contacts in SeSCs. We systematically optimize the TMO thicknesses and assess their effect on device performance under both standard AM1.5G and indoor illumination conditions. Our results demonstrate that incorporating optimized TMO layers substantially improves the fill factor (FF) and parasitic resistances of the device, leading to enhanced power conversion efficiencies (PCEs). The best outdoor performance is achieved with a 20 nm MoO HTL, delivering a champion PCE of 5.5%. For indoor conditions, a 10 nm VO HTL enables PCE values exceeding 10% across a wide range of light intensities and spectra. Ultraviolet photoelectron spectroscopy and transmission electron microscopy-energy dispersive X-ray spectroscopy analyses reveal strong interfacial interactions between Se and the TMOs, including evidence of spontaneous MoSe formation at room temperature, which likely contributes to enhanced hole selectivity and suppressed recombination. Additionally, preliminary indications suggest the possible formation of VSe under similar conditions. These findings underscore the crucial role of inorganic HTLs in unlocking the full potential of SeSCs and highlight their suitability for emerging applications such as indoor photovoltaics and monolithic tandem architectures.

The development of safe and high-performance electrolytes is essential to realize the full potential of lithium metal batteries (LMBs) for next-generation energy storage. In this study, we report the design and synthesis of composite polymer electrolytes (CPEs) based on polyoxanorbornene bottlebrush polymers (BPs) with poly-(ethylene oxide) (PEO) side chains. These unique bottlebrush architectures, synthesized via ring-opening metathesis polymerization, enable precise control over mechanical properties while maintaining a high ionic conductivity. The incorporation of copper bis-(trifluoromethanesulfonyl)-imide (Cu-(TFSI)) into the polymer matrix enhances ionic conductivity by disrupting PEO crystallinity and modifying the local lithium coordination environment. Electrochemical impedance spectroscopy revealed that the optimized CPE with 2 wt % Cu-(TFSI) exhibited a 3-fold increase in ionic conductivity compared to BPs without Cu salt incorporation. Symmetric Li|Li cells demonstrated stable cycling with low overpotential for over 500 h, highlighting the electrolyte's excellent lithium metal compatibility and dendrite suppression capabilities. Full-cell tests with LiFePO (LFP) and perylenetetracarboxylic dianhydride (PTCDA) cathodes further confirmed the electrolyte's versatility, delivering high capacities, superior rate performance, and extended cycle life compared to conventional polymer electrolytes. This work demonstrates that Cu-modified bottlebrush polymer electrolytes are a promising platform for enabling high-performance, solid-state LMBs, with broad applicability to both inorganic and organic cathodes.

The binder-active material interface failure has been a critical issue in rechargeable batteries, especially for high-performance materials with large (∼300%) volume changes. This interface is very complex and undergoes various changes over the course of fabrication to cycling in service. Here, PVdF/Si was chosen as a model interface, and the interface failure behavior is quantified in terms of critical energy release rate . Further, the effect of electrolyte and the electrochemical cycling on was quantified using an experimental method, which includes a Michelson interferometer-based optical setup coupled with a blister test in an electrochemical cell. The of the as-prepared dry PVdF/Si interface is 0.55 ± 0.10 J m, but it decreased to 0.31 ± 0.10 J m (i.e., a 40% reduction) upon introducing the electrolyte. The interface fracture property, , further reduces to 0.26 ± 0.03 J m (additional 21% decrease) due to subsequent electrochemical cycling. It was also observed that the measured is independent of sample geometry and is only a function of materials that make up the interface. The surface analysis (SEM and XPS) showed that the crack propagation in these samples occurred at the interface (i.e., neither in the PVdF nor in the Si substrate). Therefore, the reduction in is attributed to the changes in the bonding environment at the interface due to electrolyte solvents and subsequent chemical changes that occur at the interface due to electrochemical cycling.

Bismuth vanadate (BiVO) shows promise as a photoanode for water oxidation, with a relatively low band gap of 2.4 eV. However, its performance is limited by poor carrier separation and surface recombination. To address these limitations, a BiVO-CuO/CuO nanocube (NC) heterojunction was successfully developed, increasing the photogenerated oxygen evolution current density to 2.3 mA/cm at 1.23 V vs RHE, compared to 1.4 mA/cm for bare BiVO. Addition of drop-casted CuO/CuO NCs on BiVO increases both the charge injection efficiency and the charge separation efficiency to over 60% at 1.23 V vs RHE. In comparison, the addition of drop-casted CuO nanowires (NWs) to BiVO increased the charge injection efficiency to over 65%, but it only moderately increased the charge separation efficiency to 49% at 1.23 V vs RHE. These results highlight the importance of the interface between BiVO and the catalyst layer for an enhanced photocurrent. In the CuO/CuO NCs, bulk CuO likely serves as a hole-extracting heterojunction, while surface CuO likely functions as a catalyst. In contrast, the CuO NWs function primarily as a catalyst.

Iron-intercalated MoC MXene (Fe/MoC) is presented as a robust, earth-abundant electrocatalyst for ambient ammonia synthesis. An in situ HF protocol converts MoGaC MAX into few-layer MoC terminated with =O/-F groups; subsequent wet impregnation followed by mild reduction deposits 7 wt % Fe(0) as an epitaxial coating that lines the internal van der Waals galleries and simultaneously blankets the external basal planes of the MoC MXene. Aberration-corrected STEM, FFT/inverse-FFT analysis, and STEM-EDX depth profiling verify lamellar Fe domains that connect neighboring MoC sheets while preserving crystallinity. This hybrid architecture halves the charge-transfer resistance (EIS) and provides a high density of Fe sites that preferentially adsorb N over protons. In neutral 0.1 M NaSO, the optimized material achieves a Faradaic efficiency of 28.8% and an NH yield of 19.1 μmol h mg at 0.25 V vs RHE, matching or surpassing noble-metal benchmarks under ambient conditions. Operando ATR-SEIRAS detects N-N and -NH vibrations consistent with an associative pathway, and N labeling confirms the nitrogen source. The catalyst maintains stable performance for 10 h with no detectable Fe leaching. Thus, the combination of the activity of Fe overlayers with the conductive, mechanically resilient MoC framework renders a material with remarkable electrocatalytic activity for green-ammonia production.

Amorphous lithium solid electrolytes (SE) have enabled high performance lithium metal batteries, but sodium analogues are underexplored. Here, we report sodium aluminophosphate (NAPO) SEs synthesized via spin coating from aqueous solutions. Continuous, smooth, films with submicron thickness are produced after a mild annealing step. Exploration of the Na-Al-P-O phase space reveals nanocomposite materials comprising of an amorphous NAPO with crystalline NaNO domains, suggesting a Na saturation limit within the Al-P-O matrix. A maximum ionic conductivity of ≈10 S cm is achieved, with the presence of the insulating NaNO precursor necessary for high ionic conductivity. Electron microscopy, time-of-flight secondary ion mass spectrometry and optical measurements reveal that at low concentrations the NaNO phase is initially present as diffuse nanoparticle domains and at higher concentrations it forms isolated micron-sized particles. The optimal NAPO SE has an activation energy of 0.80(1) eV, a moderate reduced Young's modulus ≈30 GPa and low electronic conductivity (≈10 S cm), making these materials promising candidates for artificial solid electrolyte interphases or as solid electrolytes in sodium metal batteries.

Improving the energy density of Na-ion batteries (NIBs) requires advances in anode materials. This study investigates SbSe/Sb composite anodes, which offer better capacity and stability than the individual constituents. X-ray diffraction (XRD) revealed that (de)-sodiation is driven by synergies between the operating mechanisms of SbSe and Sb, enabling a reversible capacity of 360 mAh g (at 1000 mA g). This performance is also aided by amorphization of the sodiated phases, which promotes rapid Na-diffusion. The work emphasizes the need for continuous material and structural optimizations to fully harness their benefits for enabling efficient and fast-charging NIBs.

Perovskite solar technology stands at a pivotal juncture, marked by remarkable efficiencies reaching up to 27.3%. However, these achievements remain confined to a handful of research institutions globally, primarily attributed to the inherent challenge of stabilizing the narrow bandgap structure of FAPbI-based perovskite. This study delves into the exploration of various strategies to enhance the performance of FAPbI-based perovskite. Specifically, it scrutinizes the impact of substrate selection, annealing processes, additive incorporation, and passivation strategies. Through systematic investigation and meticulous refinement of these key parameters, we were able to obtain optimized device performance with an integrated current density of 25.59 mA cm and a power conversion efficiency up to 21.86%, starting from a reference device of 23.11 mA cm and 18.23% values for integrated current density and device efficiency, respectively. This work endeavors to propel the broader adoption and practical realization of high-performance perovskite solar technologies, thereby contributing to the sustainable advancement of renewable energy solutions.

Organic molecules for nonaqueous redox-flow batteries tend to become increasingly complex because, for practical applications, they have to fulfill several requirements in terms of redox potential, solubility, and stability. Implementing these functionalities in the design of materials often results in an undesirable high synthetic complexity, which reduces the feasibility for large-scale applications. Considering redox potential, solubility, stability, and low synthetic complexity as important design considerations, we investigated the suitability of alkyl-substituted terephthalonitriles for use as anolytes in redox-flow batteries. These derivatives can be synthesized in two steps. With one ethyl substituent, the stability is very limited because the reduced anolyte deprotonates the solvent, which then reacts with the neutral anolyte. Experiments and density functional theory calculations show that this reaction can be slowed down by introducing two alkyl substituents. In combination with dialkoxy-substituted benzene derivatives as the catholyte, 2,5-dialkylterephthalonitriles achieve >3 V flow batteries that exhibit capacity retention of >99.8% cycle and energy efficiencies of up to 77% at a current density of 40 mA cm. With these metrics, 2,5-dialkylterephthalonitriles outperform many previously reported flow batteries using benzene-based anolytes, but for future practical application, solubility and long-term stability need to be further enhanced.

The carbon dioxide reduction reaction (CORR) driven by sunlight is expected to become a sustainable way of producing high-value compounds in the future. To achieve this goal, affordable and efficient photocatalysts still need to be discovered. In this work, we show that near-IR luminescent octahedral molybdenum iodido clusters decorated with isonicotinato ligands, (BuN)[MoI(OCCHN)] (Mo), once combined with iron-doped carbon nitride (Fe--CN), provide the Mo/Fe--CN nanostructured materials, which are able to photocatalytically produce carbon monoxide (CO) from CO with high efficiency and selectivity. In a plausible mechanism, the Mo cluster acts as a photosensitizer, and its pyridine groups interact coordinatively with the embedded iron atoms, thus promoting the electronic conduction to the catalytic iron sites of the nanohybrid. The materials were characterized analytically, texturally, structurally, and spectroscopically using techniques such as inductively coupled plasma (ICP), specific surface area measurements, UV-vis-NIR diffuse reflectance spectra (DRS), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDS), and photoluminescence. The CORR studies showed that this association induces a change in the selectivity and a significant increase in CO production compared to that produced separately by the Mo clusters and graphitic precursors. Considering the versatility of this building block strategy for preparing multicomponent hybrid nanomaterials, molybdenum metal clusters are regarded as promising catalysts for creating eco-friendly and cost-effective photocatalysts for the CORR.

Solution-based deposition of high-quality inorganic compound semiconductors onto a variety of substrates is a key challenge toward integrating photovoltaic technologies into a wide range of infrastructures. CuZnSn-(S,Se) (CZTSSe) is one of the most promising solar absorbers processable by solution-based methods, however there is a substantial knowledge gap linking the chemistry of cation complexes and chalcogen precursors, e.g. thiourea (TU), to the microstructure and opto-electronic properties of the thin-films. In this study, we focus our attention on the complexation of zinc chloride (ZnCl) and zinc acetate (ZnAc) in dimethylformamide (DMF)-based CZTS precursor inks and how this ultimately affects the performance of CZTSSe thin-film devices on F/SnO (FTO) substrates. Acetate coordination not only improves the overall CZTSSe composition and structural uniformity but also lowers the zinc salt decomposition temperature, from 519 to 284 °C, which significantly affects the rate of grain growth during selenization and final microstructure. ZnAc-based CZTSSe films show densely packed grain growth due to the fast rate of selenium incorporation during annealing, while ZnCl-based CZTSSe displays slower rates due to the high decomposition temperature of ZnCl. Upon the incorporation of 25 nm Mo at the CZTSSe/FTO interface, a champion power conversion efficiency of 6.02% was achieved with ZnAc precursor salt, over two times greater than the equivalent device architecture prepared with ZnCl, at 2.62%. This investigation illustrates the significant role of the molecular complexes in tuning the grain growth kinetics and final microstructure and therefore improving device performance on semitransparent substrates.

Electrochemical reactions are highly sensitive to the physical and chemical environments near the electrodes. Thus, controlling the electrolyte ionic composition and the electrochemical potential of specific ions can modify the overpotential of electrochemical reactions and enhance their selectivity toward the desired products. Ratchet-based ion pumps (RBIPs) are membrane-like devices that utilize temporal potential modulation to drive a net ionic flux with no associated electrochemical reactions. RBIPs were fabricated by coating the surfaces of nanoporous alumina wafers with metals, forming nanoporous capacitors. Placing the RBIP between two electrolyte compartments and applying an alternating signal between the metal layers resulted in a voltage buildup across the membrane, leading to ion pumping. Here, we demonstrate that by modifying the electrochemical potential of ions, RBIPs can accelerate or inhibit electrochemical reactions on the surface of adjacent water-splitting electrodes according to the RBIP input signal. Proton pumping toward a water-splitting cathode prevented proton depletion due to the hydrogen evolution reaction and maintained the pH in the cathode compartment. The combination of ion pumping and ion selectivity can enable the electrolyte composition to be tuned near the electrodes, providing greater control over the electrochemical process.

Transition metal fluorides (TMFs) are promising alternatives for Li battery cathode active materials as they can show specific capacities up to 619 mAh/g for CrF, compared to 272 mAh/g for LiNiMnCoO, a commonly used intercalation cathode. TMFs are intrinsically difficult to study due to their incompatibility with typical liquid electrolytes and the need for conductive additives to ensure sufficient utilization. In this work, thin-film solid-state devices are used to compare six transition metals mixed with LiF in a 1.1:2 TM/LiF ratio (where TM = Cr, Mn, Fe, Co, Ni, or Cu) without the influence of additive and electrolyte interactions. C/10 delithiated capacities of 540, 113, 402, 407, 566, and 143 mAh/g are shown for (Cr, Mn, Fe, Co, Ni, Cu)-LiF cathodes, respectively. Chromium fluoride consistently outperforms the other cathodes up to 8C (190/219 mAh/g, lithiated/delithiated). Differences between the behavior of the TM-LiF cathodes are explored using electrochemical characterization and atomistic simulations. The choice of TM has a significant impact on cathode performance, which is likely to be connected to their distinct chemical natures, changing the thermodynamics and pathway of the conversion reaction.

Although many layered oxide semiconductors possess seemingly suitable band gaps for photo-(electro)-catalysis in the UV-vis range, they often exhibit low or no activity in practice. Bulk layered cesium titanate is one such example of an inactive semiconductor, where the introduction of cesium vacancies with subsequent thermal treatment leads to the activation of its photocatalytic properties. Here, we demonstrate the promising effect of cesium vacancies on the photocatalytic (PC) activity enhancement in the hydrogen evolution reaction (HER) from water in the presence of HO/MeOH (80:20). In a separate experiment, we also further prove that the Cs-vacant (V) layered titanate sample treated at 700 °C exhibits a remarkably improved photoelectrocatalytic (PEC) activity in the oxygen evolution reaction (OER) of partially exfoliated cesium titanates. In contrast, bulk cesium titanate shows no PC activity toward HER and only minimal PEC activity toward OER. Computational modeling reveals that partial interlayer Cs vacancies can increase the surface area up to 120 Å and generate interlayer voids as large as 10 Å. Furthermore, hybrid density functional theory (DFT) calculations indicate that these Cs vacancy defects lead to the formation of midgap states, which are expected to enhance photogenerated charge carrier separation and stabilization, thereby improving both PC and PEC activities. Our approach results in the development of a cocatalyst-free semiconductor light absorber capable of producing hydrogen with significantly higher efficiency than both bulk cesium titanate and protonated layered titanate.