H2 Evolution Reaction Research Articles

Precisely regulating ion convection to counteract electro-migration for H+–OH- separation with enabling efficient electrochemical water softening

Conventional electrochemical precipitation softening often suffers from the low utilization of OH– for hardness precipitation on the cathode surface in traditional undivided electrolytic cell. In this study, an asymmetric cathode was designed to confine the occurrence of H2 evolution reaction at its backside in an undivided electrolytic cell, where the electrodes were placed aslant at an angle of 5° to facilitate the upward motion of H2 bubbles and the water flowing distribution network was used to inhibit the circumfluence of water. This specific cell configuration successfully decoupled the ion convection and electro-migration behaviors, and regulated the convection behaviors of H+ and OH– to counteract their electro-migration behaviors. Specially, theoretical calculations revealed that the OH– convection rate (Vw,b = 0.033 ∼ 0.043 cm s−1) under the combined effects of H2 gas bubbling and water flowing-through cathode at current densities of 1 ∼ 15 mA cm−2 was larger than its electro-migration rate (Ve = 0.0062 ∼ 0.019 cm s−1), which effectively promoted the transport of OH– away from the cathode backside into the bulk solution opposite to the direction toward the anode side. The H+ electro-migration toward the cathode could be also offset by the convection mediated by water flowing-through anode. Thus, the H+–OH– neutralization reaction was effectively inhibited, favoring the hardness precipitation. Under the optimum condition, the developed cell showed a Ca hardness removal efficiency of 80.8 ± 1.18 % and a current efficiency of up to 73 % at an energy consumption of 2.67 ± 0.13 kWh kg−1 CaCO3, which were superior to most electrolytic systems with or without membranes. Generally, this study provides a precisely engineered electrodes configuration for energy-efficient electrochemical water softening in circulating cooling water system.

Finite Element Analysis of Local pH Variations in Electrolysis with Porous Electrodes, Considering Water Self-Ionization.

A finite element model was developed to simulate ion fluxes and local pH changes within and around porous electrodes during the H2 evolution reaction (HER) in acidic electrolytes. This model is particularly characterized by its ability to simulate scenarios in which the local pH inside and near the cathode exceeds 7, even under bulk acidic conditions (e.g., pH = 1), by considering the self-ionization of water. Steady-state calculations using meshes with an appropriate spatial distribution inside and near the cathode revealed that the relationship between the local pH and the double-layer potential at the interface between the porous catalyst layer and the electrolyte domains changed notably when the local pH exceeded the threshold of 7. By comparing the fluxes of H+ and OH- ions at the interface and using the thickness of the catalyst layer as a variable, we determined that the presence of H+ ions within the pores or the supply of OH- ions from the pores to the interface was responsible for the characteristic change in the local pH observed for the porous electrode. The porous electrode model constructed in this study can potentially serve as a basis that can be extended to a wide range of electrolysis systems, including not only the HER, but also the reduction of CO2, H2O2, and O2, and even oxidation reactions such as the O2 evolution reaction.

Anion Effect in Electrochemical CO2 Reduction: From Spectators to Orchestrators.

The electrochemical CO2 reduction reaction (eCO2RR) offers a pathway to produce valuable chemical fuels from CO2. However, its efficiency in aqueous electrolytes is hindered by the concurrent H2 evolution reaction (HER), which takes place at similar potentials. While the influence of cations on this process has been extensively studied, the influence of anions remains largely unexplored. In this work, we study how eCO2RR selectivity and activity on a gold catalyst are affected by a wide range of inorganic and carboxylate anions. We utilize in situ differential electrochemical mass spectrometry (DEMS) for real-time product monitoring coupled with molecular dynamics (MD) simulations. We show that anions significantly impact eCO2RR kinetics and eCO2RR selectivity. MD simulations reveal a new descriptor─free energy of anion physisorption─where weakly adsorbing anions enable favorable CO2 reduction kinetics, despite the negative charge carried by the electrode surface. By leveraging these fundamental insights, we identify propionate as the most promising anion, achieving nearly 100% Faradaic efficiency while showing high CO production rates that are comparable to those in bicarbonate. These insights underscore the vital role of anion selection in achieving a highly efficient eCO2RR in aqueous electrolytes.

Efficient charge abstraction and oriented accumulation driven by strong interfacial interaction facilitate photocatalytic selective oxidation of furfuralcohol coupled with H2 evolution

S-scheme heterostructures are promising strategies for photogenerated charge transport and spatial separation, yet the intrinsic mechanism of interfacial interaction on carrier dynamics remains under exploration. Herein, an S-scheme NiTiO3/Cd0.6Zn0.4S (NTO/CZS) heterostructure with strong interfacial interaction was fabricated to synchronously drive redox half-reactions. The KPFM, SPV, in-situ ESR, in-situ XPS, and fs-TA combined with and DFT simulation confirmed the reinforced IEF’s role in efficient charge abstraction and oriented accumulation on RP and OP surfaces, respectively, thereby synchronously triggering redox half-reactions. In addition, the furfuryl alcohol (FOL) to furfural (FAL) conversion was driven by αC-H bond cleavage, with H2O playing a crucial role in achieving efficient photocatalytic selective oxidation of FOL coupled with H2 evolution reaction (HER). The optimized 35 % NTO/CZS exhibited exceptional photocatalytic performance, achieving FOL selective oxidation coupled with HER, surpassing that of CZS and NTO for HER of 3.3 mmol g−1 h−1 by 6 times and 50 times, respectively. The present work provides new insights into constructing S-scheme heterostructures with strong interfacial electric field (IEF) for efficient charge abstraction and oriented accumulation to synchronously facilitate redox half-reactions.

Molten Salt Modulation of Potassium-Nitrogen-Carbon for the Breaking Kinetics Bottleneck of Photocatalytic Overall Water Splitting and Environmental Impact Reduction.

Sluggish interfacial water dissociation and the O2 evolution reaction (OER) kinetics are the main obstacles that limit the photocatalytic overall water-splitting performance. A molten salt modulation of potassium-nitrogen-carbon is herein demonstrated as the formation of highly crystalline potassium-doped poly(triazine imide) (KPTI). The in situ X-ray diffraction patterns and theoretical calculation show that the KCl melt can significantly reduce the free energy for the polycondensation of triazine building blocks owing to the formation of a kinetically stable KPTI. Benefiting from the presence of potassium-carbon-nitrogen moiety, the catalyst not only weakens the excitonic confinement to improve the separation efficiency of photogenerated charge carriers but also enhances the stability of carbon sites by suppressing the undesired C═O formation. Moreover, KPTI accelerates water dissociation by forming interfacial K·H2O clusters with an ordered structure, which supplies sufficient protons for the H2 evolution reaction and lowers the energy barrier to enhance the kinetics of OER. Therefore, a stable photocatalytic overall water-splitting performance can be achieved over KPTI with a stoichiometric generation of products (H2 and O2). Life cycle assessment shows that a carbon-neutral scenario can be achieved on KPTI production in the near term with an increase in green power in the electricity grid.

MoSe2-Sensitized Water Splitting Assisted by C60-Dendrons on the Basal Surface.

We propose a new class of H2 evolution photocatalystcontaining TMD not as a co-catalyst, but as a photosensitizer: MoSe2/C60-dendron nanohybrids, assisted by 1-benzyl-1,4-dihydronicotinamide (BNAH) as a sacrificial donor and Pt nanoparticles as co-catalysts. The 2D/0D mixed-dimensional heterojunction formed by MoSe2 and C60 is highly effective in generating mobile carriers under visible and NIR light irradiation. This process involves electron extraction from the exciton in MoSe2 to C60, followed by electron transfer to Pt nanoparticles via MV2+, leading to H2 production from water. Even NIR light, such as 800 nm light corresponding to the A-exciton absorption of MoSe2, can facilitate water splitting. The EQY of the H2 evolution reaction was estimated to be 0.0027%.

Scaling CO2 Electrolyzer Cell Area from Bench to Pilot.

To contribute meaningfully to carbon dioxide (CO2) emissions reduction, CO2 electrolyzer technology will need to scale immensely. Bench-scale electrolyzers are the norm, with active areas <5 cm2. However, cell areas on the order of 100s or 1000s of cm2 will be required for industrial deployment. Here, we study the effects of increasing cell area, scaling over 2 orders of magnitude from a 5 cm2 lab-scale cell to an 800 cm2 pilot plant-scale cell. A direct scaling of the bench-scale cell architecture to the larger area results in a ∼20% drop in ethylene (C2H4) selectivity and an increase in the parasitic hydrogen (H2) evolution reaction (HER). We instrument an 800 cm2 electrolyzer cell to serve as a diagnostic tool and determine that nonuniformities in electrode compression and flow-influenced local CO2 availability are the key drivers of performance loss upon scaling. Machining of an initial 800 cm2 cell results in a standard deviation in MEA compression that is 7-fold that of a similarly produced 5 cm2 cell (0.009 mm). Using these findings, we redesign an 800 cm2 cell for compression tolerance and increased CO2 transport and achieve an H2 FE in the revised 800 cm2 cell similar to that of the 5 cm2 case (16% at 200 mA cm-2). These results demonstrate that by ensuring uniform compression and fluid flow, the CO2 electrolyzer area can be scaled over 100-fold and retain C2H4 selectivity (within 10% of small-scale selectivity).

High Mass Transfer Rate in Electrocatalytic Hydrogen Evolution Achieved with Efficient Quasi-Gas Phase System.

The adhesion of H2 bubbles on the electrode surface is one of the main factors limiting the performance of H2 evolution of electrolytic water, especially at high current density. To overcome this problem, here a "quasi-gas phase" electrolytic water reaction system based on capillary effect is proposed for the first time to improve the mass transfer efficiency of H2. The typical feature of this reaction system is that the main site of H2 evolution reaction is transferred from the bulk aqueous solution to the gas phase environment above the bulk aqueous solution, thus effectively inhibiting the aggregation of H2 bubbles and reducing the resistance of their diffusion away. Electrochemical test results show that the proposed quasi-gas phase system can significantly reduce the potential required in H2 evolution reaction process at high current density compared with the conventional electrolytic reaction system. Specifically, the overpotential potential is reduced by 0.31 V when the H2 evolution current density of 250 mA cm-2 is achieved.

High Mass Transfer Rate in Electrocatalytic Hydrogen Evolution Achieved with Efficient Quasi‐Gas Phase System

The adhesion of H2 bubbles on the electrode surface is one of the main factors limiting the performance of H2 evolution of electrolytic water, especially at high current density. To overcome this problem, here a "quasi‐gas phase" electrolytic water reaction system based on capillary effect is proposed for the first time to improve the mass transfer efficiency of H2. The typical feature of this reaction system is that the main site of H2 evolution reaction is transferred from the bulk aqueous solution to the gas phase environment above the bulk aqueous solution, thus effectively inhibiting the aggregation of H2 bubbles and reducing the resistance of their diffusion away. Electrochemical test results show that the proposed quasi‐gas phase system can significantly reduce the potential required in H2 evolution reaction process at high current density compared with the conventional electrolytic reaction system. Specifically, the overpotential potential is reduced by 0.31 V when the H2 evolution current density of 250 mA cm‐2 is achieved.

A3B Zn(II)-Porphyrin-Coated Carbon Electrodes Obtained Using Different Procedures and Tested for Water Electrolysis

In the context of water electrolysis being highlighted as a promising technology for the large-scale sustainable production of hydrogen, the water-splitting electrocatalytic properties of an asymmetrically functionalized A3B zinc metalated porphyrin, namely, Zn(II) 5-(4-pyridyl)-10,15,20-tris(4-phenoxyphenyl)-porphyrin, were evaluated in a wide pH range. Two different electrode manufacturing procedures were employed to outline the porphyrin’s applicative potential for the O2 and H2 evolution reactions (OER and HER). The electrode, manufactured by coating the catalyst on a graphite support from a dimethylsulfoxide solution, displayed electrocatalytic activity for the OER in an acidic electrolyte. An overpotential value of 0.44 V (at i = 10 mA/cm2) and a Tafel slope of 0.135 V/dec were obtained. The modified electrode that resulted from applying a Zn(II)-porphyrin-containing catalyst ink onto the same substrate type was identified as a bifunctional water-splitting catalyst in a neutral medium. OER and HER overpotentials of 0.78 and 1.02 V and Tafel slopes of 0.39 and 0.249 V/dec were determined. This is the first Zn(II)-porphyrin to be reported as a heterogenous bifunctional water-splitting electrocatalyst in neutral aqueous electrolyte solution and is one of very few porphyrins behaving as such. The TEM analysis of the porphyrin’s self-assembly behavior revealed a wide variety of architectures.

Two nickel-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24via WO4/Sb2O bridges and Ni-O-W linkages with efficient hydrogen evolution activity.

Two Ni-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24 units via WO4/Sb2O bridges and Ni-O-W linkages, Na4H8[Ni(enMe)2][(Sb2O)2(NiW6O24)-{Ni12O2(OH)4(enMe)4(H2O)3(WO4)2(B-α-PW9O34)2}2]·39H2O (1) and H9[Ni(en)2(H2O)][Ni0.5(en)2(H2O)][Ni-(enMe)2(H2O)][(Sb2O)2(NiW6O24){Ni12O2(OH)4(en)2(enMe)2(H2O)3(WO4)2}-{Ni12O2(OH)4(en)4(H2O)3(WO4)2}(B-α-PW9O34)4]·45H2O (2), have been hydrothermally synthesized and characterized, in which the {Ni12(WO4)2(PW9)2} subunit was obtained by the synergistic directing effect of 2 lacunary PW9O34 (PW9) fragments and further linked by a central Anderson-type (Sb2O)2(NiW6O24) bridge. Both compounds represent the first example of Ni-added polyoxometalates (POMs) simultaneously based on Keggin-type and Anderson-type POM components. Photocatalytic studies revealed that 2 can work as an efficient heterogeneous catalyst towards a light-driven H2 evolution reaction, achieving a hydrogen evolution rate of as high as 19 214 μmol g-1 h-1 (TON = 1500), which is superior to most of the reported POM-based heterogeneous catalysts.

(Invited) 14.8% Quantum Efficient Gallium Phosphide Photocatalyst for Hydrogen Evolution

Gallium phosphide is a well-established photoelectrode material for H2 or O2 evolution from water, but particle-based GaP photocatalysts for H2 evolution are very rare. To understand the reasons, we investigated the photocatalytic H2 evolution reaction (HER) of suspended n-type GaP particles with iodide, sulfite, ferricyanide, ferrous ion, and hydrosulfide as sacrificial electron donors, and using Pt, RhyCr2-yO3, and Ni2P HER cocatalysts. A record AQE of 14.8% at 525 nm was achieved after removing charge trapping states from the GaP surface, adding a Ni2P cocatalyst to reduce the proton reduction overpotential, lowering the Schottky-barriers at the GaP-cocatalyst and GaP-liquid interfaces, and adjusting the electrochemical potential of the electron donor. The work showcases the main factors that control charge separation in suspended photocatalysts, and it explains why most known HER photocatalysts in the literature are based on n-type and not p-type semiconductors. Figure 1

Covalently Immobilized Anthraquinone on Carbon and Its Use As a Proton-Exchange Counter Electrode in Impurity Sensitive Electrochemical Measurements

The choice of counter electrode has emerged as an important topic in our search for non-platinum group metal (PGM) materials that can catalyze reactions that are important for fuel cells and electrolyzers such as oxygen reduction reaction (ORR), H2 evolution reaction (HER), and the CO2 reduction reaction. Recent investigations on the stability of Pt materials have revealed that significant dissolution occurs during O2 evolution, making the use of Pt as a counter electrode unsuitable for developing non-PGM materials for ORR and HER, in particular. That has led to increased use of carbon as the counter electrode, which can also oxidize at high voltages and generate partial oxidization compounds such as CO and other small organic molecules, which in turn, are detrimental to metal surfaces. Therefore, developing a stable counter electrode material is key for artifact-free electrocatalytic measurements. In this work, we will discuss the synthesis and application as a counter electrode of a proton-exchange anthraquinone-based reversible redox pair that was covalently grafted onto a high-purity (e.g. 99.99995%) carbon rod. The anthraquinone-grafted counter electrodes were evaluated in aqueous electrolytes using metal single crystals such as Pt(111) and Ir(111) surfaces as the working electrodes, given their extreme sensitivity to impurities in the electrochemical cell. Our results show that the counter electrode voltage is far more stable and centered around the proton-exchange process happening at the anthraquinone centers. This is in contrast to the wide-range voltage changes observed when using the un-grafted carbon rod. There were no differences in the single-crystal surface cyclic voltammetry profile, even after performing HER or OER, which typically causes the biggest swings in the counter electrode voltages. Lastly, there were no detectable amounts of grafted material leaching or exfoliated carbon, confirming that the use of a known redox pair such as from anthraquinone is an effective strategy to prevent artifacts in electrocatalysis research.

Low-Temperature Wastewater Electrolysis for H2 and Clean Water Generation

Water electrolysis represents a sustainable approach to produce green hydrogen (H2); however, the high energy cost (H2O → 2H+ + 2e- + ½O2, ∆H° = 275 kJ/mol H2, E° = −1.18 V) associated with water electrolysis and electricity cost (>$50/MWh) results in a minimum H2 selling price ≈$4/kg H2. Hence, we need to find alternative process to generate H2 to meet the current U.S. Department of Energy's (DOE's) Energy Earthshots of $1/kg H2 in one decade.Wastewater electrolysis represents an alternative approach to generate H2 with renewable sources by electrochemically oxidizing organic molecules to generate H2 (e.g., CH3COOH + 2H2O → 2CO2 + 8e- + 8H+, ∆H° = 53 kJ/mol, E° = −0.02 V,) which has up to 5 times lower energy requirement than water electrolysis. As opposed to water electrolysis that requires clean water streams, wastewater electrolysis uses readily available waste streams that need cleanup anyway to generate H2; hence, integrating a second application in addition to H2 generation.1-3 In this work, we compare the performance of heterogeneous electrocatalysts for the electrocatalytic oxidation (ECO) of organic molecules present in wastewater as well as electrocatalysts for the H2 evolution reaction (HER) at room temperature. ECO electrocatalysts were developed and tested using real wastewaters derived from several sources including the hydrothermal liquefaction (HTL) of food waste. We synthesized the ECO electrocatalysts using both platinum-group metals (PGM) as well as base-group metals (BGM) with equimolar loadings and tested them as a function of half-cell potential. Our results show that both PGM- and BGM-based bimetallics improve the activity and stability compared to the baseline RuO2-based catalysts4-6. We performed a preliminary techno-economic analysis and showed that the levelized costs of using this technology to process the wastewater alone is equivalent to that of traditional wastewater processing. The sale of the produced H2 co-product will decrease the levelized processing cost below that of current wastewater processing. References Andrews, E.; Lopez-Ruiz, J. A.; Egbert, J. D.; Koh, K.; Sanyal, U.; Song, M.; Li, D.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Gutiérrez, O. Y.; Holladay, J. D., Performance of Base and Noble Metals for Electrocatalytic Hydrogenation of Bio-Oil-Derived Oxygenated Compounds. ACS Sustainable Chemistry & Engineering 2020, 8 (11), 4407-4418.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. Journal of Applied Electrochemistry 2021, 51 (1), 107-118.Lopez-Ruiz, J. A.; Andrews, E.; Akhade, S. A.; Lee, M.-S.; Koh, K.; Sanyal, U.; Yuk, S. F.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Glezakou, V.-A.; Rousseau, R.; Gutiérrez, O. Y.; Holladay, J. D., Understanding the Role of Metal and Molecular Structure on the Electrocatalytic Hydrogenation of Oxygenated Organic Compounds. ACS Catalysis 2019, 9 (11), 9964-9972.Qiu, Y.; Lopez-Ruiz, J. A.; Zhu, G.; Engelhard, M. H.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic decarboxylation of carboxylic acids over RuO2 and Pt nanoparticles. Appl. Catal. B-Environ. 2022, 305, 121060.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2021, 51 (1), 107-118.Qiu, Y.; Lopez-Ruiz, J. A.; Sanyal, U.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt. Appl. Catal. B-Environ. 2020, 277, 119277. Figure 1

(Invited) Controlled Synthesis of Cocatalyst-Semiconductor Hybrid Nanomaterials for Photocatalytic Water Splitting

With the escalating global demand for energy, mitigating anthropogenic climate change necessitates the pursuit of carbon-neutral energy sources to diminish reliance on fossil fuels. Utilizing particulate photocatalysts for solar-light-driven water splitting presents a promising and sustainable paradigm for the large-scale production of storable and clean H2 fuel. To improve the solar energy conversion efficiency, coupling the photocatalysts with cocatalysts is a broadly adopted approach not only to facilitate charge separation and transport but also to serve as reaction sites and accelerate water-splitting reactions. Recent breakthroughs in colloidal synthesis enable the fabrication of advanced nanoparticles with precise control over size and composition. Colloidal NPs represent ideal cocatalyst candidates due to their capacity to provide numerous active sites and facilitate uninterrupted light absorption by the semiconductor. Here, we introduce our approach to synthesize cocatalyst-semiconductor hybrids as efficient photocatalysts, including the alloying of platinum group metal nanoparticle cocatalysts and the control of single-atom cocatalyst locations on semiconductor nanoparticles.Platinum group metals exhibit high efficiency as cocatalysts in the hydrogen evolution reaction, attributed to their favorable catalytic and electronic properties. Bimetallic alloy systems, in general, can considerably modulate their electronic structures, resulting in exceptional physicochemical properties surpassing those of their monometallic counterparts. Herein, we synthesized PtRu solid-solution alloy nanoparticles as high-performance H2 evolution reaction cocatalysts. The rational integration of PtRu nanoparticles with Al-doped SrTiO3 photocatalyst through liquid-phase adsorption and successive two-step annealing ensure the uniform deposition of PtRu alloy nanoparticles with a solid-solution structure. The bimetallic synergy between Pt and Ru induces higher electrocatalytic activity for the hydrogen evolution reaction and a superior electron-capturing property than its Pt counterpart. Modification of Al-doped SrTiO3 with PtRu alloy nanoparticles, CrOx, and CoOOH results in efficient photocatalytic overall water-splitting activity with an apparent quantum yield of 65% at 365 nm. This work introduces a framework to elucidate catalytic trends, offering rational design guidance for the development of bimetallic solid-solution nanoparticles as highly active cocatalysts for overall water splitting.Single-atom cocatalysts dispersed on semiconductor materials exhibit outstanding heterogeneous catalytic properties through the interactions between the single atoms and the photocatalyst. The nature of these interactions depends on whether the single atoms are located on the surface or within the interior of the photocatalyst. In this work, the location-selective placement of single atoms is achieved by carefully adjusting experimental procedure. Using CdSe nanoplatelets as a support, applying different Pt precursor complexes, solvent, and workup process resulted in location selective deposition of Pt atoms outside/inside CdSe nanoplatelet support. In photocatalytic hydrogen evolution reaction, the surface-adsorbed single Pt atoms exhibit higher stability than the substituted ones. This study provides a viable strategy for the structurally precise synthesis and design of single-atom catalysts.

(Invited) Energy-Efficient and Impurity-Tolerant Electrochemical Co-Generation of Acid and Base Solutions

The sequential application of acid and base solutions can be used to perform chemical transformations that are of interest for carbon management and sustainable resource utilization, including CO2 capture, CO2 removal, production of slaked lime, and recovery of critical minerals. Electrochemical co-generation of acid and base from salt solutions enables their use in closed-loop processes that could be powered by renewable electricity, wherein acid and base are regenerated from the salt byproduct of their application. To be viable at scale, acid-base co-generating systems need to be energy-efficient and tolerant to impurities that are inevitably released into recycle loops. Conventional electrochemical methods for co-generating acid and base, such as bipolar membrane electrodialysis (BPMED), rely on the use of ion exchange membranes (IEMs) to inhibit H+ and OH– recombination, but IEMs cause large resistive losses that severely limit the energy efficiency and current density of these systems. In addition, cation exchange membranes (CEMs) do not tolerate polyvalent cations (e.g., Ca2+, Mg2+) in the presence of base, yet polyvalent cations are intrinsic to all high-impact applications. In this talk, I will describe our development of acid-base co-generating systems in which H+ and OH– recombination is inhibited by competitive transport of supporting electrolyte and H+ masking, which enables the use of a simple porous diaphragm separator instead of IEMs. We developed an ion transport model to predict the current efficiency for acid-base co-generation as a function of the electrolyte composition and operating parameters. Instead of a bipolar membrane, our systems use the H2 oxidation reaction (HOR) and H2 evolution reaction for H+ and OH– generation, respectively. We demonstrate IEM-free production of acid and base at useful concentrations in the presence of polyvalent cations with much higher energy efficiency and current density than state of the art BPMED systems. Individual cells can be stacked by combining HOR and HER electrodes into bipolar gas diffusion electrodes that recirculate H2 with near-unity efficiency. To demonstrate the utility of the acid and base solutions generated by this system, I will describe their use to extract Mg(OH)2 from ultramafic rocks for application in CO2 removal.

Joule heating assisted solvothermal growth of C3N4 on carbon paper for effective photothermal-photocatalytic water splitting for hydrogen evolution

Photocatalysis combined with photothermal effect has become a promising process for highly-efficiently production of H2. In this work, C3N4 was solvothermally grown on carbon paper and further construction of vacancies by fast Joule heating treatment. The substrate carbon paper could increase the photothermal evaporation of water, and the fabricated vacancies could accelerate the charge separation. Furthermore, the temperature increased because of the photothermal synergistic effect, which was favorable for the H2 evolution reaction. Based on the above, the CP/SCN-NVs system achieved efficient H2 evolution in deionized water without sacrificial agent and precious metal co-catalysts, with a hydrogen evolution rate of 2248.83 μmol m-2 h−1, which was 41.3 times higher than the C3N4 suspension system. Overall, this work offered a new approach for efficient H2 evolution in photothermal-photocatalytic dual-phase systems.

Stable and efficient hydrogen evolution activity of tungsten-incorporated nanocrystalline perovskite BaSnO3 electrocatalyst

The increasing demand in energy consumption and alarming environmental concern is compelling to develop alternative renewable and clean energy sources. Hydrogen (H2) is identified as a potential candidate due to its abundance, high gravimetric energy density, and no carbon footprint. Presently, splitting of water is a highly promising method for sustainable hydrogen generation, and the key challenge is to develop a stable and high-performing electrocatalysts for H2 evolution reaction (HER) as a renewable energy source. Metal oxides are excellent alternative electrocatalysts to noble metals due to their cost effectiveness, tunability and abundance. Ternary perovskite barium stannate (BaSnO3) has been intensely explored for water splitting and electrocatalysis related applications. Tungsten (W) 1 % incorporated BaSnO3 synthesized by facile hydrogen peroxide route is explored as an electrocatalyst for HER activity in acidic medium for the first time. The pure and W-incorporated BaSnO3 exhibited promising HER activity with an overpotential value of 233 and 295 mV at 10 mA/cm2 with enhanced electrochemical surface area of 7.309 and 3.075 Fcm−2, respectively. A 12-hour stability test not only concluded the durability and performance of H2 evolution activity but also confirmed the enhanced initial current density for the W-incorporated BaSnO3 sample.

A Schottky/Z-Scheme Hybrid for Augmented Photocatalytic H2 and H2O2 Production.

The prodigious employment of fossil fuels to conquer the global energy demand is becoming a dreadful threat to the human society. This predicament is appealing for a potent photocatalyst that can generate alternate energy sources via solar to chemical energy conversion. With this interest, we have fabricated a ternary heterostructure of Ti3C2 nanosheet modified g-C3N4/Bi2O3 (MCNRBO) Z-scheme photocatalyst through self-assembly process. The morphological analysis clearly evidenced the close interfacial interaction between g-C3N4 nanorod, Bi2O3 and Ti3C2 nanosheets. The oxygen vacancy created on Bi2O3 surface, as suggested by XPS and EPR analysis, supported the Z-scheme heterojunction formation between g-C3N4 nanorod and Bi2O3 nanosheets. The collaborative effect of Z-scheme and Schottky junction significantly reduced charge transfer resistance promoting separation efficiency of excitons as indicated from PL and EIS analysis. The potential of MCNRBO towards photocatalytic application was investigated by H2O2 and H2 evolution reaction. A superior photocatalytic H2O2 and H2 production rate for MCNRBO is observed, which are respectively around 5 and 18 folds higher as compared to pristine CNR nanorod. The present work encourages for the development of a noble, eco-benign and immensely efficient dual heterojunction based photocatalyst, which can acts as saviour of human society from energy crisis.

Electrocatalytic Performance of 2D Monolayer WSeTe Janus Transition Metal Dichalcogenide for Highly Efficient H2 Evolution Reaction.

Nowadays, the development of clean and green energy sources is the priority interest of research due to increasing global energy demand and extensive usage of fossil fuels, which create pollutants. Hydrogen has the highest energy density by weight among all chemical fuels. For the commercial-scale production of hydrogen, water electrolysis is the best method, which requires an efficient, cost-effective, and earth-abundant electrocatalyst. Recent studies have shown that the 2D Janus transition metal dichalcogenides (JTMDs) are promising materials for use as electrocatalysts and are highly effective for electrocatalytic H2 evolution reaction (HER). Here, we report a 2D monolayer WSeTe JTMD, which is highly effective toward HER. We have studied the electronic properties of 2D monolayer WSeTe JTMD using the periodic hybrid DFT-D method, and a direct electronic band gap of 2.39 eV was obtained. We have explored the HER pathways, mechanisms, and intermediates, including various transition state (TS) structures (Volmer TS, i.e., H*-migration TS, Heyrovsky TS, and Tafel TS) using a molecular cluster model of the subject JTMD noted as W10Se9Te12. The present calculations reveal that the 2D monolayer WSeTe JTMD is a potential electrocatalyst for HER. It has the lowest energy barriers for all the TSs among other TMDs. It has been shown that the Heyrovsky energy barrier (= 8.72 kcal mol-1) in the case of the Volmer-Heyrovsky mechanism is larger than the Tafel energy barrier (= 3.27 kcal mol-1) in the Volmer-Tafel mechanism. Hence, our present study suggests that the formation of H2 is energetically more favorable via the Volmer-Tafel mechanism. This study helps to shed light on the rational design of 2D single-layer JTMD, which is highly effective toward HER, and we expect that the present work can be further extended to other JTMDs to find out the improved electrocatalytic performance.