Effect of ZrO2 on the performance of Co–CeO2 catalysts for hydrogen production from waste-derived synthesis gas using high-temperature water gas shift reaction

In this study, highly active and stable CeO₂, ZrO₂, and Zr_(1-x)Ce_(x)O₂-supported Co catalysts were prepared using the co-precipitation method for the high-temperature water gas shift reaction to produce hydrogen from waste-derived synthesis gas. The physicochemical properties of the catalysts were investigated by carrying out Brunauer-Emmet-Teller, X-ray diffraction, CO-chemisorption, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and H₂-temperature-programmed reduction measurements. With an increase in the ZrO₂ content, the surface area and reducibility of the catalysts increased, while the interaction between Co and the support and the dispersion of Co deteriorated. The Co–Zr_0.4Ce_0·6O₂ and Co–Zr_0.6Ce_0·4O₂ catalysts showed higher oxygen storage capacity than that of the others because of the distortion of the CeO₂ structure due to the substitution of Ce⁴⁺ by Zr⁴⁺. The Co–Zr_0.6Ce_0·4O₂ catalyst with high reducibility and oxygen storage capacity exhibited the best catalytic performance and stability among all the catalysts investigated in this study.     

Synthesis of binary Co–Mg–O oxide system and study of its behavior in reduction/oxidation cycling

The nanoscale Co–Mg–O oxide sample (15 wt% in terms of Co₃O₄) was prepared from the corresponding xerogel synthesized by the modified sol-gel method. The hydrolysis of as-prepared Mg(OCH₃)₂ was carried out using the aqueous solution of Co(NO₃)₂ precursor. The CoO_x nanocrystallites of about 10–20 nm in size were shown to be uniformly distributed within the MgO matrix. The reduction of Co–Mg–O in H₂ flow was found to proceed in two separate stages within the temperature ranges of 200–350 °C and 350–600 °C. The prepared binary Co–Mg–O system was demonstrated to possess completely reproducible reduction behavior in the consecutive reduction/reoxidation cycles. The phase composition of the sample exposed to both the reducing and oxidative environment was followed by an in situ X-ray diffraction analysis performed at temperatures of 25, 300, 500 and 700 °C. The determined lattice parameters for MgO (a = 4.219 Å) and Co₃O₄ (a = 8.110 Å) were found to be slightly increased as compared with the values from Powder Diffraction File, so that the formation of joint non-stoichiometric (Mg_1-xCo_x)O and (Co_3-xMg_x)O₄ phases was suggested. The strong chemical interaction of cobalt oxide with MgO matrix was also evidenced by the data of a diffuse reflectance UV–vis spectroscopy.     

The BaCeO3-based composite protonic conductors prepared by Spark Plasma Sintering (SPS) and free-sintering methods

The poor chemical stability and unsatisfactory electrical conductivity of the BaCeO₃-based protonic conductors may be improved by doping, by the creation of solid solutions (e.g. with BaZrO₃) or by the formation of composite materials. In this work, the latter approach was used and the BaCe_0·9Y_0·1O₃ – (Ba–Ce–Y–Si–P–O) composites were synthesized and investigated. The BaCe_0·9Y_0·1O₃ host material and the modifier phase (6 wt%) powders were mixed by mechanical homogenization. The sintering of compacted powders was done using Spark Plasma Sintering (SPS) and the free-sintering (FS) methods, followed by the post-annealing of some samples. The influence of the sintering method and the presence of the modifier phase on the phase composition, crystallographic structure, microstructure and electrical properties were investigated. A strong influence of the sintering method on these properties was found. Also, the introduction of the modifier phase leads to considerable changes in phase composition, which are dependent on the sintering method and the post-annealing treatment. The electrical properties, determined in different gas atmospheres using the Electrochemical Impedance Spectroscopy (EIS) technique, were correlated with the phase composition and microstructure changes. The minor increase of electrical conductivity due to the introduction of the modifier phase was observed only in the case of SPS sintered samples. A detailed discussion of the observed correlations including the possible chemical composition and structural changes, mutual reactivity, amorphization, the removal of residual stress and the detailed analysis of the EIS results was done. The formation of BaCe_0·9Y_0·1O₃ – (Ba–Ce–Y–Si–P–O) composite materials using the Spark Plasma Sintering method was found to be a promising approach towards ceramic protonic conductors with improved properties.     

Effect of B-site Al substitution on hydrogen production of La0.4Sr0.6Mn1-xAlx (x=0.4, 0.5 and 0.6) perovskite oxides

Thermochemical water splitting using perovskite oxides as redox materials is one of the important way to use solar energy to produce green hydrogen. Thus, it is hence important to discover new materials that can be used for this purpose. In this regard, we focused on Al-substituted La_0.4Sr_0.6Mn_1-xAl_xO₃ (x = 0.4, 0.5 and 0.6) perovskite oxides, namely as La_0.4Sr_0.6Mn_0.6Al_0.4 (LSMA4664), La_0.4Sr_0.6Mn_0.5Al_0.5 (LSMA4655), and La_0.4Sr_0.6Mn_0.4Al_0.6 (LSMA4646) which have been successfully synthesized. Herein, synthesized LSMA4664, LSMA4655, and LSMA4646 were subjected to three consecutive thermochemical cycles in order to determine their oxygen capacity, hydrogen capacity, re-oxidation capability and structural stability following three cycles. Thermochemical cycles were carried out at 1400 °C for reduction and 800 °C for the oxidation reaction. LSMA4646 exhibited the highest O₂ production capacity with 275 μmol/g among the other perovskites employed in the study. Moreover, LSMA4646 has also the highest H₂ production, 144 μmol/g, with 90% of re-oxidation capability by the end of three thermochemical water splitting cycles. On the other hand, LSMA4664 has the lowest H₂ production and only kept approximately one-third of its hydrogen production capacity by the end of cycles. Thus, the current study provides insight that the increase in the Al-substitution enhances both oxygen and hydrogen production capacity. Besides, increasing the Al amount increases the structural stability during the redox reactions, the re-oxidation capability was also increased from 38% to 89% after thermochemical cycles.     

Facial synthesis of p-p heterojunction composites: Evaluation of their electrochemical properties with photovoltaics-electrolyzer water splitting using two-electrode system

Mixed transition metal oxides have garnered widespread interest as alternative electrocatalysts for the oxygen and hydrogen generation reactions; however, they tend to require extended synthetic routes, in addition to possessing limited electrocatalytic activities and stabilities. Herein, we report the observation of a synergistic effect between the non-precious metal oxides Mn₃O₄ and Co₃O₄ with CuO and NiO, wherein the resulting composites exhibit promising properties as catalysts for the alkaline water electrolysis process. The activities of these composites in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) were improved compared to their counterparts, and the dynamic potentials of these processes were reduced. Importantly, low overpotentials of 202 and 380 mV were found for the CuO–Mn₃O₄ composite catalysts for the OER and the HER at 10 mA/cm², respectively. In addition, electrochemical impedance spectroscopy measurements showed a reduced impedance response for the composites, which was dominated by the relaxation of the intermediate frequency associated with the adsorption of the intermediate. Furthermore, the superior catalytic activities of the composites were attributed to their structural properties, high electroactive surface areas, fast electron transport kinetics, and good chemo-electrical bonding between Mn₃O₄ and CuO. Importantly, merging with a marketable silicon-based solar cells, the accumulated PV-EC water splitting device obtains greater hydrogen production under stimulated solar light irradiation. This work offers a typical demonstration and respected strategies for practical large-scale solar H₂ production via an economical PV-EC technology.     

Enhancing resistance of carbon deposition and reaction stability over nickel loaded fibrous silica-alumina (Ni/FSA) for dry reforming of methane

Syngas production from the dry reforming of methane is now the most extensively utilized method for removing massive amounts of greenhouse emissions. Effective solutions towards the utilization of greenhouse gases such as CO₂ and CH₄ are scarce, except for power generation in the energy sector, which is a major source of CO₂. Herein, dry reforming of methane was experimented for the first time using an effective catalytic system composed of 5% Ni fibrous silica-alumina (FSA) that was successfully fabricated using a hydrothermal method. The characterization results from XRD, FESEM mapping, TEM, BET,XRF, FTIR, H₂-TPR, TGA/DTA, and Raman spectra demonstrated that Ni/FSA is composed of orderly Ni dispersion, small particles of Ni, robust basic sites, and high oxygen vacancies which enhanced the catalytic efficiency. The synthesized Ni/FSA also reduced coke formation and had long-term stability with no evidence of inactivation during and after the catalytic cycles. The superior activity of Ni/FSA was manifested in the high conversion rates of CH₄ and CO₂ at 97% and 92% respectively, with a H₂:CO ratio of ≈ 1. The stability of Ni/FSA was also sustained over 30 h of operation at 800 °C. The findings of the Raman, TEM, and TGA/DTA tests revealed that the spent Ni/FSA catalysts did not exhibit graphitic carbon or metal sintering in significant amounts when compared to commercial Ni–Si/Al catalysts.     

Turning glycerol surplus into renewable syngas through glycerol steam reforming over a sol-gel Ni–Mo2C-Al2O3 catalyst

In this work, a sol-gel Ni–Mo₂C–Al₂O₃ catalyst is employed for the first time in the glycerol steam reforming for syngas production. Catalyst stability and activity are investigated in the temperature range of 550 °C–700 °C and time on stream up to 30 h. As reaction temperature increases, from 550 °C to 700 °C, H₂ yield boosts from 22% to 60%. The stability test, carried out at milder conditions (600 °C and Gas-Hourly Space-Velocity (GHSV) of 50,000 mL h⁻¹.g_cat⁻¹), shows high catalyst stability, up to 30 h, with final conversion, H₂ yield, and H₂/CO ratio of 95%, 53% and 1.95, respectively. Both virgin and spent catalysts have been characterized by a multitude of techniques, e.g., Atomic-Absorption spectroscopy, Raman spectroscopy, N₂-adsorption-desorption, and Transmission Electron Microscopy (TEM), among others. Regarding the spent catalysts, carbon deposits’ morphology becomes more graphitic as the reaction temperature increases, and the total coke formation is mitigated by increasing reaction temperature and lowering GHSV.     

Novel sonochemical synthesis of Zn2V2O7 nanostructures for electrochemical hydrogen storage

Although utilization of diverse classes of metal oxides as hydrogen storage materials has been reported, but there is still a major need to introduce efficient materials. Herein, mesoporous Zn₂V₂O₇ nanostructures were produced by a new sonochemical method using hydrazine, zinc nitrate, and ammonium vanadate as the starting reagents and then annealed at 700 °C. Prior to annealing, Zn₃V₃O₈ was produced in the presence of ultrasonic waves, whereas in the absence of ultrasonic waves, Zn₂(VO₄)₂ was the major product. In fact, ultrasonic waves interfered with the reaction mechanism and reduced V⁵⁺ to V⁴⁺ and V³⁺. Because of the proper composition and structure of these nanostructures, they were used for electrochemical storage of hydrogen. Storage of over 2899 mAh/g after 20 cycles by flower-like nanostructures revealed their high capability. The results also showed that morphology affects efficiency such that three-dimensional spherical nanostructures had a storage capacity of 2247 mAh/g after 20 cycles.     

Hydrogen production from additive-free formic acid over highly active metal organic frameworks-supported palladium-based catalysts

The metal organic frameworks (MOFs) supported Pd catalysts for H₂ generation from formic acid (FA) were synthesized in this work, via a facile excessive impregnation-low temperature reduction approach. Among the synthetic catalysts, 10% Pd/MOF-Cr (18) displayed a remarkable performance for catalyzing FA dehydrogenation in additive-free aqueous solution, and the corresponding TOF_mid achieved 537.8 h^?1 at 323 K. Furthermore, the bimetallic Ni–Pd alloy catalysts were prepared by the introduction of Ni in the subsequent work. Fortunately, 10% Ni_0.4Pd_0.6/MOF-Cr was found to be a highly active and fairly durable catalyst, exhibiting a TOF_mid as high as 737.9 h^?1 at 323 K with almost 100% X_FA (final) and S_H2, and remained 94% of its original activity in the third cyclic catalysis. Meanwhile, Ni was discovered to be indispensable in increasing the electron density of Pd, downsizing the immobilized metal particles and inhibiting the agglomeration of the loaded nanoparticles.     

Enhanced hydrogen storage performance of Cu3(BTC)2 in situ inserted with few-layer silicon-based nanosheets

Silicon-based nanosheets (SNS) were synthesised via a mild (60 °C) and time-saving (8 h) modified topochemical method. Then, Cu₃(BTC)₂ and SNS@Cu₃(BTC)₂ were successfully synthesised by microwave irradiation, and their characteristics and hydrogen storage performance were analysed by multiple techniques. The accordion-like SNS exhibited void spaces, a unique low buckled structure, and ultrathin, almost transparent, loosely stacked layers with a high specific surface area (362 m²/g). After in-situ synthesis with Cu₃(BTC)₂, the SNS compound achieved a high specific surface area (1526 m²/g), outstanding hydrogen storage performance (5.6 wt%), and a desirable hydrogen diffusion coefficient (10^?7). Thus, SNS doping improved the hydrogen storage performance of Cu₃(BTC)₂ by 64% through electron transfer reactions with Cu enabled by the unique composite nanostructure of SNS@Cu₃(BTC)₂. This study presents a promising method of synthesising SNS and porous composite materials for hydrogen storage.     

Steam reforming of acetic acid for hydrogenproduction: Catalytic performances of Ni and Co supported on Ce0·75Zr0·25O2 catalysts

The catalytic steam reforming of acetic acid over both Ni/ and Co/Ce_0·75Zr_0·25O₂ (CZO) catalysts in the temperature range of 450–650 °C and steam-to-carbon molar ratios of 3–9 was studied. It was found that the complete acetic acid conversion was achieved for all the conditions investigated. Nevertheless, the C–C bond cleavage conversion was attained less than the acetic acid conversion at a given condition due to carbon deposition on the catalyst. However, hydrogen yield was obtained in the same trend as C–C bond cleavage conversion as well. The results revealed that the CZO as an active support prefers to promote the ketonization reaction to the C-C bond cleavage reaction at a lower temperature, and vice versa at a higher temperature. The Ni/CZO catalyst exhibits higher C–C bond cleavage conversion than the Co/CZO catalyst particularly at 650 °C whereas the Co/CZO catalyst is more active for ketonization reaction at low temperatures. However, as an increase in reaction temperature, the Co/CZO catalyst promotes ketonization reaction more pronouncedly toward aldol-condensation reaction thus giving rise to the carbon deposition. The results deduced from the effect of space velocity on the activity and product distribution suggested that the steam reforming of acetic acid over Ni/CZO catalyst is dominated by decomposition of acetic acid, while that of Co/CZO catalyst by ketonization reaction.     

Dark fermentative biohydrogen production using pretreated Scenedesmus obliquus biomass under an integrated paradigm of biorefinery

In recent times, biohydrogen production from microalgal feedstock has garnered considerable research interests to sustainably replace the fossil fuels. The present work adapted an integrated approach of utilizing deoiled Scenedesmus obliquus biomass as feedstock for biohydrogen production and valorization of dark fermentation (DF) effluent via biomethanation. The microalgae was cultivated under different CO₂ concentration. CO₂-air sparging of 5% v/v supported maximum microalgal growth and carbohydrate production with CO₂ fixation ability of 727.7 mg L^?1 d^?1. Thereafter, lipid present in microalgae was extracted for biodiesel production and the deoiled microalgal biomass (DMB) was subjected to different pretreatment techniques to maximize the carbohydrate recovery and biohydrogen yield. Steam heating (121 °C) in coherence with H₂SO₄ (0.5 N) documented highest carbohydrate recovery of 87.5%. DF of acid-thermal pretreated DMB resulted in maximum H₂ yield of 97.6 mL g^?1 VS which was almost 10 times higher as compared to untreated DMB (9.8 mL g^?1 VS). Subsequent utilization of DF effluent in biomethanation process resulted in cumulative methane production of 1060 mL L^?1. The total substrate energy recovered from integrated biofuel production system was 30%. The present study envisages a microalgal biorefinery to produce biohydrogen via DF coupled with concomitant CO₂ sequestration.     

CuCo2O4–NiO heterostructure catalysts for hydrogen production from ammonia borane

Ammonia borane (NH₃BH₃, AB) has been considered as one of the most attractive candidates for chemical hydrogen-storage materials and chemical hydrogen generation materials. Development of low-cost and high-performance catalysts for hydrogen generation from AB is highly desirable, which is still a huge challenge. Hollow sphere CuCo₂O₄ promotes the catalytic hydrolysis of AB due to its unique hollow sphere shape and the synergistic effect of Co and Cu elements. In this study, a heterogeneous structured catalyst containing NiO and CuCo₂O₄ was developed by a simple and low-cost method in order to improve the catalytic performance of CuCo₂O₄. Initially, CuCo₂O₄ with hollow sphere structure was synthesized by hydrothermal method, and then NiO were deposited onto CuCo₂O₄ by impregnation-calcination method to form a heterogeneous structure. The CuCo₂O₄–NiO catalyst showed good catalytic activity for the hydrolysis of AB. The catalytic performance of CuCo₂O₄–NiO was then optimised by controlling the concentration of the impregnated salt solution, and the optimised catalytic performance was 1.42 times that of pure CuCo₂O₄ with a HER value of 870 mL_H2g_cat⁻¹min⁻¹. This low-cost CuCo₂O₄–NiO obtained by impregnation-calcination method is valuable for catalytic hydrogen production from AB.     

Preparation and improvement of nickel catalyst supported ordered mesoporous spherical silica for thermocatalytic decomposition of methane

The thermocatalytic alteration of CH₄ into highly pure hydrogen and filaments of carbon was investigated on a series of Ni-catalysts with various contents (25, 40, 55, and 70 wt%) supported mesoporous spherical SiO₂. The silica with ordered structure and high specific surface area (1136 m²/g) was synthesized using the Stöber technique with TEOS as a silica precursor and CTAB as the template in a simple synthesis system of aqueous-phase. This technique led to the preparation of mesoporous spherical silica. The prepared samples were characterized using BET, TPR, XRD, TPO, and SEM analyses. The prepared catalysts with different nickel loading showed the BET surface area ranging from 225.0 to 725.7 m²/g. These results indicated that an increase in nickel content decreases the surface area and leads to a subsequent collapse of a pore structure. SEM analysis confirmed a spherical nanostructure of catalysts and revealed that with the increase in loading of Ni, the particle size enlarged, because of the agglomeration of the particles. The results implied that the high methane conversion of 54% obtained over the 55 wt% Ni/SiO₂ at 575 °C and this sample had higher stability at lower reaction temperature than the other prepared catalysts, slowly deactivation was observed for this catalyst at a period of 300 min of time on stream.     

Titanate quantum dots-sensitized Cu2S nanocomposites for superficial H2 production via photocatalytic water splitting

TiO₂ quantum dots-sensitized Cu₂S (Cu₂S/TiO₂) nanocomposites with varying concentration of TiO₂ QDs are synthesized via a facile two-stage hydrothermal-wet impregnation method. X-ray diffraction analysis confirms the formation of Cu₂S and TiO₂with chalcocite and anatase phases, respectively. The observed shoulder-like absorption peaks indicate the UV–visible light-driven properties of the composite. Morphological analysis reveals that the fabricated Cu₂S/TiO₂ composite consists of Cu₂S with a nano rod-like shape (average length and width of ～856 and ～213 nm, respectively) and nanosheets-like structures (average length and width of ～283 and ～289 nm, respectively), whereas the TiO₂ is formed as quantum dots with a size range of 8.2 ± 0.4 nm. Chemical state analysis shows the presence of Cu⁺, S^2?, Ni²⁺, and O^2? in the nanocomposite. The H₂ evolution rate over the optimized photocatalyst is found to be ～45.6 mmol h^?1g^?1_cat under simulated solar irradiation, which is around 5 and 2.4-fold higher than that of the pristine TiO₂ and Cu₂S, respectively. Continuous H₂ production for 30 h is achieved during time-on-stream experiments, demonstrating the excellent stability and durability of the Cu₂S/TiO₂ photocatalyst for large-scale applications.     

Nickel-loaded red mud catalyst for steam gasification of bamboo sawdust to produce hydrogen-rich syngas

Ni/red mud (RM) catalysts were prepared by wet impregnation and used in the catalytic steam gasification of bamboo sawdust (BS) to produce hydrogen-rich syngas. The system was optimized in terms of the amount of added nickel (10%), reaction temperature (800 °C), and catalyst placement (separately behind the BS). The maximum H₂ yield was 17.3% higher than that using pure RM catalyst and 43.8% higher than that of BS gasification alone, and the H₂/CO ratio in the syngas reached 7.82. This Ni/RM catalyst also retained good activity after six cycles in a double-stage fixed bed reactor. Analysis using X-ray fluorescence, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and other methods revealed that the interaction of Ni, Fe, and Mg in Ni/RM produced bimetallic compounds containing active sites, such as NiFe₂O₄, MgNiO₂, and NiO. This explains the good catalytic performance in the tar conversion during the gasification process.     

Producing hydrogen from the fermentation of cheese whey and glycerol as cosubstrates in an anaerobic fluidized bed reactor

This study aimed to evaluate the effect of the organic loading rate (OLR) (60, 90, and 120 g Chemical Oxygen Demand (COD). L^?1. d^?1) on hydrogen production from cheese whey and glycerol fermentation as cosubstrates (50% cheese whey and 50% glycerol on a COD basis) in a thermophilic fluidized bed reactor (55 °C). The increase in the OLR to 90 gCOD.L^?1. d^?1 favored the hydrogen production rate (HPR) (3.9 L H₂. L^?1. d^?1) and hydrogen yield (HY) (1.7 mmol H₂. gCOD^?1_app) concomitant with the production of butyric and acetic acids. Employing 16S rRNA gene sequencing, the highest hydrogen production was related to the detection of Thermoanaerobacterium (34.9%), Pseudomonas (14.5%), and Clostridium (4.7%). Conversely, at 120 gCOD.L^?1. d^?1, HPR and HY decreased to 2.5 L H₂. L^?1. d^?1 and 0.8 mmol H₂. gCOD^?1_app, respectively, due to lactic acid production that was related to the genera Thermoanaerobacterium (50.91%) and Tumebacillus (23.56%). Cofermentation favored hydrogen production at higher OLRs than cheese whey single fermentation.     

Performance analysis of metal hydride based simultaneous cooling and heat transformation system

The performance of metal hydrides based simultaneous cooling and heat transformation system (MHCHT) using a combination of La_0.9Ce_0.1Ni₅–MmNi_4.4Al_0.6–MmNi_3.7Co_0.7Mn_0.3Al_0.3 hydrides is evaluated. The MHCHT is thermodynamically analysed using statically and dynamically measured PCIs and thermodynamic properties. In addition, a set of governing equations is solved in order to study the heat and hydrogen transfer between the reaction beds. The experimental PCI measurement data are compared with the numerical results and a reasonably good agreement is observed between them. From the results, the slope and hysteresis factors are determined for further thermal analyses. It is observed that the performance parameters i.e. cooling capacity, heat transformation capacity and coefficient of performance (COP) of MHCHT are significantly decreased by 42.4%, 26.7% and 19.1% respectively when dynamic property data are considered compared to static property data. In addition, the thermodynamic cycle is analysed by considering the variation in pressure during hydrogen transfer process between the metal hydride beds.     

Steam reforming of 1-methylnaphthalene over pure CeO2 under model coke oven gas conditions containing high H2S concentrations

Tar and H₂S are obstacles to the efficient production of H₂ from unused industrial gases and biomass gasification gases. Robust catalysts against tar and H₂S are required to produce H₂ from such resources. Herein, a stable steam reforming reaction is demonstrated over pure CeO₂ under reaction conditions consisting of ~2 vol% 1-methylnaphthalene and ~1000 ppm H₂S. The presence of H₂S significantly suppressed Ni/MgO/Al₂O₃ activity and increased carbon deposition, regardless of the steam to carbon (S/C) ratio. In contrast, the promotion or suppression of CeO₂ activity in the presence of H₂S was dependent on the S/C ratio. At S/C = 1.2, H₂S deactivated the CeO₂ catalyst and increased carbon deposition. Conversely, H₂S promoted the reforming reaction and decreased carbon deposition on CeO₂ at S/C ≥ 2.0. The results of this study clarify that pure CeO₂ exhibits outstanding and stable activity for the steam reforming reaction of 1-methylnaphthalene in the presence of H₂S by controlling the S/C of the inlet gas.     

CoMo heterohierarchical foam-structured cathode for anion exchange membrane water electrolyzer

It is important to consider the synergy of heterostructures to improve the slow kinetics of water dissociation in the alkaline hydrogen evolution reaction (HER). Herein, we report a simple method to design a heterohierarchical CoMo catalyst. The CoMo catalyst was prepared by simple one-pot electrodeposition on carbon paper (CP). The CoMo/CP catalyst was optimized for the alkaline HER by controlling the electrodeposition bath conditions, potential, and time. The optimized catalyst shows the heterohierarchical structure containing the electrically conductive metallic Co in the bulk and Mo-incorporated Co containing Mo⁴⁺ at the surface. It exhibited a lower HER overpotential of 0.11 V at ?20 mA/cm² compared to those of the others owing to the synergetic effect of the between the Co and Mo incorporated Co. The results highlight the advantages of the simple method developed herein for the design of heterohierarchical catalysts.