Niobium-doped cobalt phosphide nanowires realizing enhanced electrocatalytic activity for overall water splitting

Designing cost-effective bifunctional catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline electrolyte remains a significant challenge. Herein, we report adding Nb to pristine CoP nanowires enhances the material's catalytic activities towards HER and OER. Density functional theory (DFT) calculation unravels that the Nb atoms not only optimize hydrogen binding abilities on CoP surface, but also modulate the surface electron densities of in situ formed β-CoOOH during anodic oxidation, thereby greatly accelerate both the HER and OER kinetics in alkaline solutions. In addition, an alkaline electrolyzer using Nb-doped CoP nanowires as cathode and anode for overall water splitting, delivers 100 mA cm^?2 at low cell voltage of 1.70 V, superior to Pt//RuO₂ couple. This doping strategy can be extended to other transition metal phosphides as multifunctional catalysts towards overall water splitting and beyond.     

A new cathodic electrode deposit with palladium nanoparticles for cost-effective hydrogen production in a microbial electrolysis cell

Microbial electrolysis cell (MEC) provides a sustainable way for hydrogen production from organic matters, but it still suffers from the lack of efficient and cost-effective cathode catalyst. In this work carbon paper coated with Pd nanoparticles was prepared using electrochemical deposition method and used as the cathodic catalyst in an MEC to facilitate hydrogen production. The electrode coated with Pd nanoparticles showed a lower overpotential than the carbon paper cathode coated with Pt black. The coulombic efficiency, cathodic and hydrogen recoveries of the MEC with the Pd nanoparticles as catalyst were slightly higher than those with a Pt cathode, while the Pd loading was one order of magnitude less than Pt. Thus, the catalytic efficiency normalized by mass of the Pd nanoparticles was about fifty times higher than that of the Pt black catalyst. These results demonstrate that utilization of the cathode with Pd nanoparticles could greatly reduce the costs of the cathodic catalysts when maintaining the MEC system performance.     

Application of density functional theory and machine learning in heterogenous-based catalytic reactions for hydrogen production

Various feedstocks such as natural gas, glycerol, biomass, methanol, ethane, and other hydrocarbons can be reformed to generate hydrogen as a viable alternative source of renewable energy. Also, hydrogen is generated via other processes not associated with reforming including electrolysis, thermolysis, and photolysis. The reforming of the different feedstock for hydrogen reaction generally requires the utilization of heterogeneous catalysts to speed up the reactions and reduce the energy used up in the reaction. Experimental studies provide an understanding of the reaction mechanism and the nature of the reactants and products of the reaction. Computational studies involving density functional theory provide even greater insights into these reactions. Its combination with machine learning provides huge potentials for the study and discovery of technologies for hydrogen production but remains underutilized. The use of both computational techniques has widely been adjudged as the most economical and precise means of screening multiple catalysts in the heterogeneous reactions involved in hydrogen production processes. This paper reviews the application of density functional theory and machine learning in thermochemical reactions associated with the production of hydrogen. It also highlights the state-of-the-art computational methodologies employed in the design of hydrogen production technologies such as methane pyrolysis, steam methane reforming, dry reforming of methane, and other reforming processes for hydrogen production. The current progress and knowledge gaps in the research and development of hydrogen production technologies from a computational point of view are also discussed.     

Nanoengineered Zn-modified Nickel Sulfide (NiS) as a bifunctional electrocatalyst for overall water splitting

Developing an efficient and inexpensive electrocatalyst is of paramount importance for realizing the green hydrogen economy through electrocatalytic water splitting. Here, we demonstrated a facile large-scale, industrially viable binder-free synthesis of Zn-doped NiS electrocatalyst on bare nickel foam (NF) through a hydrothermal technique. The present catalyst, i.e., nickel sulfide (NiS) nanosheets on nickel foam with optimized doping of Zn atom (Zn–NiS-3), displays excellent catalytic efficacy for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It requires an overpotential of 320 mV for OER at a current density of 50 mA cm⁻² and an overpotential of 208 mV for HER at a current density of 10 mA cm⁻². The water electrolyser device having Zn–NiS-3 electrocatalyst as both cathode and anode show excellent performance, requiring a cell voltage of only 1.71 V to reach a current density of 10 mA cm⁻² in an alkaline media. The density functional theory (DFT) based calculations showed enhanced density of states near Fermi energy after Zn doping in NiS and attributed to the enhanced catalytic activities. Thus, the present study demonstrates that Zn–NiS-3@NF can be coined as a viable electrocatalyst for green hydrogen production.     

Biohydrogen production from sugar industry effluents using nickel based electrode materials in microbial electrolysis cell

Biohydrogen production from sugar industry effluents in a dual chamber microbial electrolysis cell (MEC) was investigated in this study. The MEC reactor was operated with different effluents as a substrate from cane sugar and raw sugar reprocessing units of sugar industry. The biohydrogen production was investigated using different cathode materials of Nickel plate, Nickel foam, Stainless Steel mesh. The performance of MEC was tested based on the production of hydrogen, coloumbic efficiency, hydrogen recovery and COD removal efficiency respectively. The MEC hydrogen productions revealed that cane sugar effluent was more effective as compared to raw sugar effluent. The experimental results showed that at an applied voltage of 1.0 V, Ni-foam exhibited maximum hydrogen production of 1.59 and 1.43 mmol/L/D in cane sugar and raw sugar effluents respectively, which was about twice than SS-mesh and 1.2 times Ni-plate. This study shows that Ni-foam is one of the potential candidate as low cost electrode for improving hydrogen production in MEC technology with the treatment of industrial effluents.     

Doping sp-hybridized B atoms in graphyne supported single cobalt atoms for hydrogen evolution electrocatalysis

Electrochemical water splitting to hydrogen is considered as a promising approach for clean H₂ production. However, developing highly active and inexpensive electrocatalysts is an important part of the hydrogen evolution reaction (HER). Herein, we present a multifaceted atom (sp²-and sp-hybridized boron) doping strategy to directly fine-modify the electronic structures of the active site and the HER performance by the density functional theory calculations. It is found that the binding strength between the Co atom and the B doped graphyne nanosheets can be enhanced by doping B atoms. Meanwhile, the Co@B₁-GY and Co@B₂-GY catalysts exhibit good thermodynamic stability and high HER catalytic activity. Interestingly, the Co@B₂-GY catalyst has an ideal HER performance with the ΔG_H* value of −0.004 eV. Moreover, the d-band center of the Co atoms is upshifted by the sp²-or sp-hybridized B dopants. The concentrations of the sp-hybridized B atoms have a positive effect on the electrons transformation of the Co atoms. The interaction between the H and Co atoms becomes strong with the increase of the concentrations of the sp-hybridized B atoms and thus the corresponding catalysts show sluggish HER kinetics. This investigation could provide useful guidance for the experimental groups to directly and continuously control the catalytic activity towards HER by precisely doping multifaceted atoms.     

Enhancing biohydrogen production from sugar industry wastewater using metal oxide/graphene nanocomposite catalysts in microbial electrolysis cell

Biohydrogen production through Microbial Electrolysis Cell (MEC) has drifted towards the development of suitable cost-effective cathode catalysts. In this study, two graphene hybrid metal oxide nanocomposites were used as catalysts to investigate hydrogen production in the MEC operated with sugar industry wastewater as substrate against phosphate buffer catholyte. Electrochemical characterizations exposed the better performance of NiO.rGO coated cathode which showed lesser overpotential at 600 mV and overall lowest resistance in the Nyquist plots than Ni-foam and Co₃O₄.rGO cathodes. The experimental results showed that at an applied voltage 1.0 V, NiO.rGO nanocomposite had exhibited maximum hydrogen production rate of 4.38 ± 0.11 mmol/L/D, Coloumbic efficiency of 65.6% and Cathodic hydrogen recovery of 20.8% respectively. The MEC performance in terms of biohydrogen production was 1.19 and 2.68 times higher than Co₃O₄.rGO and uncoated Ni-Foam. Hence, economical hybrid nanocomposite catalysts were demonstrated in MEC using industrial effluent for energy and environment sustainability.     

Theoretical study the component and facet dependence of HER performance on nickel phosphides surfaces

Energy depletion and environmental pollution are still serious challenges for human beings. The application of hydrogen energy should be a promising strategy to address this issue. However, the hydrogen production should be one shortcoming for hydrogen energy. The hydrogen evolution reaction (HER) based on electrocatalysis is an effective way to enhance the hydrogen generation with small energy consumption under ambient conditions. Many works have been devoted to develop high performance catalysts to satisfy the HER processes. Nevertheless, the mechanism about facet-dependence and composition-dependence influence is still need to deeply study. Hereon, based on density functional theory calculations, the [100], [110], and [111] facets of Ni_xP_y (Ni₃P, Ni₂P, NiP, NiP₂, NiP₃) systems were created and their HER catalytic activity were used to reveal the underline mechanism. By analyzing the variation of Gibbs free energy, it was found that the structural composition has a greater effect on HER than the facet. Significantly, the Ni₂P(111) surface with Ni/P-termination has the best HER performance for all samples in present work. Through exploring the electron transfer of H with surrounding atoms during the HER process, the H adsorption mechanism as well as its reaction mechanism has been revealed. The deep insights in this work provide an important fundamental that the contents of non-metal for compounds catalysts can heavily influence the performance of HER, which should give more guidance for designing new catalysts.     

Bibliometric and content analysis on emerging technologies of hydrogen production using microbial electrolysis cells

Microbial electrolysis cell (MEC) is a promising and significant approach for hydrogen production, owing to the low energy consumption and high yield/recovery efficiency. In this review, bibliometric analysis has been conducted on current research trends of MECs, followed by the content analysis of the direction and strategy for improving the hydrogen production to enlarge MECs’ applicability. Results show that energy concerns are the primary focus in MEC studies, and particular attention has been paid to decreasing internal resistance and hydrogen diffusion that may be crucial for the improvement of the yield of hydrogen production and recovery. Moreover, this study particularly reviews the development of the cathode catalysts and explores the applicability of different MEC configurations, including single-and two-chamber MECs with different kind of membranes. It also identifies the potential advantages of porous membranes as a separator in MECs and discusses the porous membrane, in conjunction with advancing hydrogen-harvesting approaches, is crucial for the improvement of hydrogen production. Finally, capital cost of MECs has been necessarily discussed, which would be significant, valuable, and beneficial to the academic research and the industrial community.     

Novel nanostructured electrocatalysts for hydrogen evolution reaction in neutral and weak acidic solutions

Microbial electrolysis cells (MECs) provide an innovative bioelectrochemical approach for hydrogen production using microorganisms as biocatalysts. The development of cost-effective cathodes for near-neutral pH and ambient temperature conditions is the most critical challenge for the practical application of MEC technology. In this study, the electrocatalytic properties of electrodeposited onto carbon felt NiFe-, NiFeP- and NiFeCoP-nanostructures towards HER in neutral and weak acidic solutions were investigated. The voltage needed to initiate hydrogen production and the current production rates were estimated from obtained linear voltammograms. The developed composite materials possess much higher catalytic activity than bare carbon felt. The highest current production rate corresponding to 1.7 ± 0.1 m³H₂/day/m² was achieved with NiFeCoP/carbon felt electrodes. In addition, the applied modifications result in improvement of the corrosion resistance. The obtained results demonstrate that Ni-based nanomodified materials are promising electrocatalysts for HER in near-neutral electrolytes and could be applied as cathodes in MECs.     

Heterostructured Co3O4/VO2 nanosheet array catalysts on carbon cloth for hydrogen evolution reaction

Developing highly efficient, low-cost, and robust water splitting hydrogen production catalysts is critical for hydrogen energy applications. This study presents the synthesis of Co₃O₄/VO₂ heterogeneous nanosheet structures on carbon cloth (Co₃O₄/VO₂/CC). The obtained Co₃O₄/VO₂/CC hybrid catalyst has a low overpotential of 108 mV at a current density of 10 mA cm^?2, a Tafel slope of 98 mV dec^?1, and high stability in 1.0 M KOH for 10 h. The experimental results and density functional theory (DFT) calculations results also show that Co₃O₄ coupled with VO₂ in Co₃O₄/VO₂/CC can optimize hydrogen adsorption energy and facilitate electron transport, thereby accelerating the catalytic kinetics for hydrogen evolution reaction (HER). This work also provided an alternative method to design and construct non-noble metal oxide-based catalysts for alkaline hydrogen production.     

Bimetallic metal-organic framework derived electrocatalyst for efficient overall water splitting

The development of bifunctional catalysts that can be applied to both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is widely regarded as a key factor in the production of sustainable hydrogen fuel by electrochemical water splitting. In this work, we present a high-performance electrocatalyst based on nickel-cobalt metal-organic frameworks for overall water splitting. The as-obtained catalyst shows low overpotential to reaches the current density of 10 mA cm⁻² with 249 mV for OER and 143 mV for HER in alkaline media, respectively. More importantly, when the electrolyzer was assembled with the as-prepared catalyst as anode and cathode simultaneously, it demonstrates excellent activity just applies a potential of 1.68 V to achieve 10 mA cm⁻² current density for overall water splitting.     

Nitrogen doped graphene supported Pd as hydrogen evolution catalyst for electrochemical methanol reformation

Electrochemical methanol reformation (ECMR) method has been identified as one of the most effective method for on-site hydrogen production. However, concentrated research towards the development of efficient inexpensive hydrogen evolution reaction (HER) electrocatalyst holds the pivotal role in realizing the hydrogen economy. In this context, for the first time N-graphene supported Pd (Pd/NG) was synthesised and employed as an HER catalyst in ECMR process. N-graphene was synthesised by modified Hummer's method followed by Pd deposition through hydrothermal route. The electrocatalytic activity of Pd/NG for hydrogen evolution was evaluated by CV and LSV techniques. Tafel slope of Pd/NG and Pt/C was calculated from LSV curves and was found to be 33 and 31 mV/decade, respectively. Exchange current density was found to be 3.6 and 3.2 × 10⁻⁴ A cm⁻² for Pd and Pt catalysts, respectively. The enhanced electrocatalytic activity is majorly attributed to the N-doping and uniform distribution of Pd nano particles on graphene. Further, the performance of Pd/NG was also evaluated in single ECMR cell using Pt–Ru/C at anode and Pd/NG at cathode as electrocatalysts. The results indicated the suitability of Pd/NG as cathode electrocatalyst for HER in ECMR process.     

Hydrogen production in single-chamber tubular microbial electrolysis cells using non-precious-metal catalysts

Platinum has excellent catalytic capabilities and is commonly used as cathode catalyst in microbial electrolysis cells (MECs). Its high cost, however, limits the practical applications of MECs. In this study, precious-metal-free cathodes were developed by electrodepositing NiMo and NiW on a carbon-fiber-weaved cloth material and evaluated in electrochemical cells and tubular MECs with cloth electrode assemblies (CEA). While similar performances were observed in electrochemical cells, NiMo cathode exhibited better performances than NiW cathode in MECs. At an applied voltage of 0.6 V, the MECs with NiMo cathode accomplished a hydrogen production rate of 2.0 m³/day/m³ at current density of 270 A/m³ (12 A/m²), which was 33% higher than that of the NiW MECs and slightly lower than that of the MECs with Pt catalyst (2.3 m³/day/m³). At an applied voltage of 0.4 V, the energy efficiencies based on the electrical energy input reached 240% for the NiMo MECs. These results demonstrated the great potential of using carbon cloth with Ni-alloy catalysts as a cathode material for MECs. The enhanced MEC performances also demonstrate the scale-up potential of the CEA structure, which can significantly reduce the electrode spacing and lower the internal resistance of MECs, thus increasing the hydrogen production rate.     

Hydrogen gas production with Ni,Ni–Co and Ni–Co–P electrodeposits as potential cathode catalyst by microbial electrolysis cells

The development of efficient and economical cathode, operating at ambient temperature and neutral pH is a crucial challenge for microbial electrolysis cell (MEC) to become commercialize hydrogen production technology. In the present work, eight different electrodes are prepared by the electroplating of Ni, Ni–Co and Ni–Co–P on two base metals i.e., Stainless Steel 316 and Copper separately to use as cathode in MEC. Electrodeposited cathode materials have been characterized by XRD, XPS, FESEM, EDX and linear voltammetry. The fabricated cathodes show higher corrosion stability with improved electro-catalytic performance for the hydrogen production in the MECs as compared to the bare cathodes (SS316 and Cu). Data obtained from linear voltammetry and MEC experiments show that developed cathode possess four times higher intrinsic catalytic activity in comparison to bare cathode. Electrodeposited cathodes are intensively examined in membrane-less MEC, operating under applied voltage of 0.6 V in batch mode at 30 ± 2 °C temperature, in neutral pH with acetate as substrate and activated sludge as inoculum. Ni–Co–P electrodeposit on Stainless Steel 316 cathode gives maximum hydrogen production rate of 4.2 ± 0.5 m³(H₂)m⁻³d⁻¹, columbic efficiencies 96.9 ± 2%, overall hydrogen recovery 90.3 ± 4%, overall energy efficiency 241.2 ± 5%, volumetric current density 310 ± 5 Am⁻³. The net energy recovery and COD removal are 4.25 kJ/gCOD and 61%, respectively. Prepared cathodes show stable performance for continuous 5 batch cycle operations in MEC.     

An overview of cathode material and catalysts suitable for generating hydrogen in microbial electrolysis cell

Bio-electrohydrogenesis through Microbial Electrolysis Cell (MEC) is one of the promising technologies for generating hydrogen from wastewater through degradation of organic waste by microbes. While microbial activity occurs at anode, hydrogen gas is evolved at the cathode. Identifying a highly efficient and low cost cathode is very important for practical implication of MEC. In this review, we have summarized the efforts of different research groups to develop different types of efficient and low cost cathodes or cathode catalysts for hydrogen generation. Among all the materials used, stainless steel, Ni alloys Pd nanoparticle decorated cathode are worth mentioning and have very good efficiency. Industrial application of MEC should consider a balance of availability and efficiency of the cathode material.     

Graphene pillared with hybrid fullerene and nanotube as a novel 3D framework for hydrogen storage: A DFT and GCMC study

A new-type 3D pillared graphene framework with hybrid fullerene and nanotube pillars (PGF-hFN) has been created depended on density functional theory (DFT) and first-principles molecular dynamics simulations (MD). It is proved to have excellent thermal structural stability. The average adsorption energy of Li is 2.77 eV much higher than the metal cohesive energy excluding lithium aggregation problem. From DFT calculations, for Li-decorated B-doped PGF-hFN, the hydrogen gravimetric density (HGD) is as high as 12.92 wt% and the according volumetric uptake is 96.4 g/L with an average adsorption energy of 0.195 eV per H₂. Further grand canonical Monte Carlo (GCMC) simulations predict 7.2 wt% in excess HGD and 53.8 g/L in excess volumetric hydrogen density at near ambient temperature (233 K) and 100 bars with the ideal adsorption enthalpy which have exceeded the 2020 the U.S. Department of Energy (DOE) ultimate target for mobile applications. Our multiscale theoretical simulations indicate this new pillared structure should be a promising carrier accessible for sorption of hydrogen molecules.     

Optimization of NiMo catalyst for hydrogen production in microbial electrolysis cells

Non-platinum based cathodes were recently developed by electrodepositing NiMo on carbon cloth, which demonstrated good electrocatalytic activity for hydrogen evolution in microbial electrolysis cells (MECs). To further optimize the electrodeposition condition, the effects of electrolyte bath composition, applied current density, and duration of electrodeposition were systematically investigated in this study. The developed NiMo catalysts were characterized with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and evaluated using chronopotentiometry and in MECs. The optimal condition for electrodeposition of NiMo on carbon cloth was determined as: a Mo/Ni mass ratio of 0.65 in electrolyte bath, an applied current density of 50 mA/cm² and electrodeposition duration of 10 min. Under this condition, the NiMo catalyst has a formula of Ni₆MoO₃ with a nodular morphology. The NiMo loading on the carbon cloth was reduced to 1.7 mg/cm² and the performance of MEC with the developed NiMo cathode was comparable to that with Pt cathode with a similar loading. This result indicates that a much lower cathode fabrication cost can be achieved compared to that using Pt catalyst, and thereby significantly enhancing the economic feasibility of the MEC technology.     

Investigating hydrogen evolution reaction properties of a new honeycomb 2D AlC

The hydrogen due to its high mass energy density is a new renewable, economically viable and clean resource. The most eco-friendly and economical approaches for the generation of hydrogen through hydrogen evolution is electrochemical water splitting. The two-dimensional (2D) nanomaterials have been recently found as potential candidates as non-noble metal catalyst for hydrogen evolution. In this work, we have systematically studied the structural and electronic properties of the newly predicted hexagonal-aluminium carbide monolayer (h-AlC ML) under the framework of dispersion-corrected density functional theory (DFT) calculations. The calculated electronic total density of states (TDOS) of h-AlC ML predict its metallic nature in contrast to other polar honeycomb 2D materials which are either semiconducting or semimetallic. The metallic behavior of h-AlC monolayer which motivates us to investigate its HER activity results due to the presence of delocalized charge density near Fermi level. Thus, we have investigated the HER activity of h-AlC ML by calculating hydrogen (H) adsorption energy (ΔE_H) and Gibbs free energy (ΔG_H) at three different sites of the 3 × 3 and 4 × 4 supercells of h-AlC ML; top of carbon atom (E_H-C), top of aluminium atom (E_H-Al) and hollow site (E_H-Hollow). Our results show that the hollow site is most catalytically active site in both supercells of h-AlC ML. We believe that our results will inspire experimentalists to fabricate this new 2D material for achieving the desired range of HER activity.