Ultrasmall Cells Research Articles

Small archaea may form intimate partnerships to maximize their metabolic potential.

DPANN archaea have characteristically small cells and unique genomes that were long overlooked in diversity surveys. Their reduced genomes often lack essential metabolic pathways, requiring symbiotic relationships with other archaeal and bacterial hosts for survival. Yet a long-standing question remains, what is the advantage of maintaining ultrasmall cells. A recent study by Zhang et al. examined genomes of DPANN archaea from marine oxygen deficient zones (ODZs) (I. H. Zhang, B. Borer, R. Zhao, S. Wilbert, et al., mBio 15:e02918-23, 2024, https://doi.org/10.1128/mbio.02918-23). Surprisingly, these genomes contain a broad array of metabolic pathways including genes predicted to be involved in nitrous oxide (N2O) reduction. However, N2O levels are likely too low in ODZs to make this metabolically feasible. Modeling co-localization of DPANN archaea (N2O consumers) with other larger cells (N2O producers) demonstrates that N2O uptake rates can be optimized by maximizing the producer-to-consumer size ratio and proximity of consumer cells to producers. This may explain why such a diversity of archaea maintain extremely small cell sizes.

Self‐Encapsulated Ni Nanoparticles on Delignified Wood Carbon for Efficient Urea‐Assisted Hydrogen Production

AbstractDeveloping efficient, low‐cost electrocatalysts for industrial‐level hydrogen production remains a significant challenge. Here lattice‐distorted Ni nanoparticles (NPs) encapsulated within a nitrogen‐doped carbon shell on delignified wood carbon (Ni‐NC@DWC) are constructed through a chitosan‐induced assembly and the pyrolysis process. Experimental and theoretical results indicate that the lattice distortion due to strong metal‐support interactions, boosts electron transfer and reaction intermediate adsorption/desorption, enhancing both the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). Interestingly, the active center Ni3+‐O is dynamically cyclically generated during the UOR. When utilized as a self‐standing electrode in an alkaline electrolyte, the Ni‐NC@DWC exhibits low potentials of 24 mV and 1.244 V at 100 mA cm−2 for HER and UOR, respectively. Moreover, the Ni‐NC@DWC achieves an ultrasmall cell voltage of 1.13 V at 100 mA cm−2 for urea‐assisted water splitting and can operate stably over 1000 h. Furthermore, when it is self‐assembled as an anion exchange membrane (AEM) electrolyzer, it requires only 1.62 V at 2000 mA cm−2 for industrial urea‐assisted water splitting and operates stably for 150 h without degradation, confirming that it is highly attractive for economical, sustainable, and scalable hydrogen production.

N-linked protein glycosylation in Nanobdellati (formerly DPANN) archaea and their hosts.

Members of the kingdom Nanobdellati, previously known as DPANN archaea, are characterized by ultrasmall cell sizes and reduced genomes. They primarily thrive through ectosymbiotic interactions with specific hosts in diverse environments. Recent successful cultivations have emphasized the importance of adhesion to host cells for understanding the ecophysiology of Nanobdellati. Cell adhesion is often mediated by cell surface carbohydrates, and in archaea, this may be facilitated by the glycosylated S-layer protein that typically coats their cell surface. In this study, we conducted glycoproteomic analyses on two co-cultures of Nanobdellati with their host archaea, as well as on pure cultures of both host and non-host archaea. Nanobdellati exhibited various glycoproteins, including archaellins and hypothetical proteins, with glycans that were structurally distinct from those of their hosts. This indicated that Nanobdellati autonomously synthesize their glycans for protein modifications probably using host-derived substrates, despite the high energy cost. Glycan modifications on Nanobdellati proteins consistently occurred on asparagine residues within the N-X-S/T sequon, consistent with patterns observed across archaea, bacteria, and eukaryotes. In both host and non-host archaea, S-layer proteins were commonly modified with hexose, N-acetylhexosamine, and sulfonated deoxyhexose. However, the N-glycan structures of host archaea, characterized by distinct sugars such as deoxyhexose, nonulosonate sugar, and pentose at the nonreducing ends, were implicated in enabling Nanobdellati to differentiate between host and non-host cells. Interestingly, the specific sugar, xylose, was eliminated from the N-glycan in a host archaeon when co-cultured with Nanobdella. These findings enhance our understanding of the role of protein glycosylation in archaeal interactions.IMPORTANCENanobdellati archaea, formerly known as DPANN, are phylogenetically diverse, widely distributed, and obligately ectosymbiotic. The molecular mechanisms by which Nanobdellati recognize and adhere to their specific hosts remain largely unexplored. Protein glycosylation, a fundamental biological mechanism observed across all domains of life, is often crucial for various cell-cell interactions. This study provides the first insights into the glycoproteome of Nanobdellati and their host and non-host archaea. We discovered that Nanobdellati autonomously synthesize glycans for protein modifications, probably utilizing substrates derived from their hosts. Additionally, we identified distinctive glycosylation patterns that suggest mechanisms through which Nanobdellati differentiate between host and non-host cells. This research significantly advances our understanding of the molecular basis of microbial interactions in extreme environments.

Uncultivated DPANN archaea are ubiquitous inhabitants of global oxygen-deficient zones with diverse metabolic potential.

Archaea from the DPANN (Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanoarchaeota, and Nanohaloarchaeota) superphylum have diverse metabolic capabilities and participate in multiple biogeochemical cycles. While metagenomics and enrichments have revealed that many DPANN are characterized by ultrasmall genomes, few biosynthetic genes, and episymbiotic lifestyles, much remains unknown about their biology. We report 33 new DPANN metagenome-assembled genomes originating from the three global marine oxygen-deficient zones (ODZs), the first from these regions. We survey DPANN abundance and distribution within the ODZ water column, investigate their biosynthetic capabilities, and report potential roles in the cycling of organic carbon, methane, and nitrogen. We test the hypothesis that nitrous oxide reductases found within several ODZ DPANN genomes may enable ultrasmall episymbionts to serve as nitrous oxide consumers when attached to a host nitrous oxide producer. Our results indicate DPANN archaea as ubiquitous residents within the anoxic core of ODZs with the potential to produce or consume key compounds.

Autotrophic biofilms sustained by deeply sourced groundwater host diverse bacteria implicated in sulfur and hydrogen metabolism

BackgroundBiofilms in sulfide-rich springs present intricate microbial communities that play pivotal roles in biogeochemical cycling. We studied chemoautotrophically based biofilms that host diverse CPR bacteria and grow in sulfide-rich springs to investigate microbial controls on biogeochemical cycling.ResultsSulfide springs biofilms were investigated using bulk geochemical analysis, genome-resolved metagenomics, and scanning transmission X-ray microscopy (STXM) at room temperature and 87 K. Chemolithotrophic sulfur-oxidizing bacteria, including Thiothrix and Beggiatoa, dominate the biofilms, which also contain CPR Gracilibacteria, Absconditabacteria, Saccharibacteria, Peregrinibacteria, Berkelbacteria, Microgenomates, and Parcubacteria. STXM imaging revealed ultra-small cells near the surfaces of filamentous bacteria that may be CPR bacterial episymbionts. STXM and NEXAFS spectroscopy at carbon K and sulfur L2,3 edges show that filamentous bacteria contain protein-encapsulated spherical elemental sulfur granules, indicating that they are sulfur oxidizers, likely Thiothrix. Berkelbacteria and Moranbacteria in the same biofilm sample are predicted to have a novel electron bifurcating group 3b [NiFe]-hydrogenase, putatively a sulfhydrogenase, potentially linked to sulfur metabolism via redox cofactors. This complex could potentially contribute to symbioses, for example, with sulfur-oxidizing bacteria such as Thiothrix that is based on cryptic sulfur cycling. One Doudnabacteria genome encodes adjacent sulfur dioxygenase and rhodanese genes that may convert thiosulfate to sulfite. We find similar conserved genomic architecture associated with CPR bacteria from other sulfur-rich subsurface ecosystems.ConclusionsOur combined metagenomic, geochemical, spectromicroscopic, and structural bioinformatics analyses of biofilms growing in sulfide-rich springs revealed consortia that contain CPR bacteria and sulfur-oxidizing Proteobacteria, including Thiothrix, and bacteria from a new family within Beggiatoales. We infer roles for CPR bacteria in sulfur and hydrogen cycling.8FE2mu4H1cxgQVBqjGxsC2Video

Arming Ru with Oxygen-Vacancy-Enriched RuO2 Sub-Nanometer Skin Activates Superior Bifunctionality for pH-Universal Overall Water Splitting.

Water electrolysis has been expected to assimilate the renewable yet intermediate energy-derived electricity for green H2 production. However, current benchmark anodic catalysts of Ir/Ru-based compounds suffer severely from poor dissolution resistance. Herein, an effective modification strategy is proposed by arming a sub-nanometer RuO2 skin with abundant oxygen vacancies to the interconnected Ru clusters/carbon hybrid microsheet (denoted as Ru@V-RuO2 /C HMS), which can not only inherit the high hydrogen evolution reaction (HER) activity of the Ru, but more importantly, activate the superior activity toward the oxygen evolution reaction (OER) in both acid and alkaline conditions. Outstandingly, it can achieve an ultralow overpotential of 176/201mV for OER and 46/6mV for the HER to reach 10mA cm-2 in acidic and alkaline solution, respectively. Inspiringly, the overall water splitting can be driven with an ultrasmall cell voltage of 1.467/1.437V for 10mA cm-2 in 0.5m H2 SO4 /1.0m KOH, respectively. Density functional theory calculations reveal that armoring the oxygen-vacancy-enriched RuO2 exoskeleton can cooperatively alter the interfacial electronic structure and make the adsorption behavior of hydrogen and oxygen intermediates much close to the ideal level, thus simultaneously speeding up the hydrogen evolution kinetics and decreasing the energy barrier of oxygen release.

Hyperactive nanobacteria with host-dependent traits pervade Omnitrophota

Candidate bacterial phylum Omnitrophota has not been isolated and is poorly understood. We analysed 72 newly sequenced and 349 existing Omnitrophota genomes representing 6 classes and 276 species, along with Earth Microbiome Project data to evaluate habitat, metabolic traits and lifestyles. We applied fluorescence-activated cell sorting and differential size filtration, and showed that most Omnitrophota are ultra-small (~0.2 μm) cells that are found in water, sediments and soils. Omnitrophota genomes in 6 classes are reduced, but maintain major biosynthetic and energy conservation pathways, including acetogenesis (with or without the Wood-Ljungdahl pathway) and diverse respirations. At least 64% of Omnitrophota genomes encode gene clusters typical of bacterial symbionts, suggesting host-associated lifestyles. We repurposed quantitative stable-isotope probing data from soils dominated by andesite, basalt or granite weathering and identified 3 families with high isotope uptake consistent with obligate bacterial predators. We propose that most Omnitrophota inhabit various ecosystems as predators or parasites.

Ultra-small bacteria and archaea exhibit genetic flexibility towards groundwater oxygen content, and adaptations for attached or planktonic lifestyles

Aquifers are populated by highly diverse microbial communities, including unusually small bacteria and archaea. The recently described Patescibacteria (or Candidate Phyla Radiation) and DPANN radiation are characterized by ultra-small cell and genomes sizes, resulting in limited metabolic capacities and probable dependency on other organisms to survive. We applied a multi-omics approach to characterize the ultra-small microbial communities over a wide range of aquifer groundwater chemistries. Results expand the known global range of these unusual organisms, demonstrate the wide geographical range of over 11,000 subsurface-adapted Patescibacteria, Dependentiae and DPANN archaea, and indicate that prokaryotes with ultra-small genomes and minimalistic metabolism are a characteristic feature of the terrestrial subsurface. Community composition and metabolic activities were largely shaped by water oxygen content, while highly site-specific relative abundance profiles were driven by a combination of groundwater physicochemistries (pH, nitrate-N, dissolved organic carbon). We provide insights into the activity of ultra-small prokaryotes with evidence that they are major contributors to groundwater community transcriptional activity. Ultra-small prokaryotes exhibited genetic flexibility with respect to groundwater oxygen content, and transcriptionally distinct responses, including proportionally greater transcription invested into amino acid and lipid metabolism and signal transduction in oxic groundwater, along with differences in taxa transcriptionally active. Those associated with sediments differed from planktonic counterparts in species composition and transcriptional activity, and exhibited metabolic adaptations reflecting a surface-associated lifestyle. Finally, results showed that groups of phylogenetically diverse ultra-small organisms co-occurred strongly across sites, indicating shared preferences for groundwater conditions.

Widespread but Poorly Understood Bacteria: Candidate Phyla Radiation.

Candidate Phyla Radiation (CPR) bacteria is a bacterial division composed mainly of candidate phyla bacteria with ultra-small cell sizes, streamlined genomes, and limited metabolic capacity, which are generally considered to survive in a parasitic or symbiotic manner. Despite their wide distribution and rich diversity, CPR bacteria have received little attention until recent years, and are therefore poorly understood. This review systematically summarizes the history of CPR research, the parasitic/symbiotic lifestyle, and the ecological distribution and unique metabolic features of CPR bacteria, hoping to provide guidance for future ecological and physiological research on CPR bacteria.

Atomically Thin Synapse Networks on Van Der Waals Photo-Memtransistors.

A new type of atomically thin synaptic network on van der Waals (vdW) heterostructures is reported, where each ultrasmall cell (≈2nm thick) built with trilayer WS2 semiconductor acts as a gate-tunable photoactive synapse, i.e., a photo-memtransistor. A train of UV pulses onto the WS2 memristor generates dopants in atomic-level precision by direct light-lattice interactions, which, along with the gate tunability, leads to the accurate modulation of the channel conductance for potentiation and depression of the synaptic cells. Such synaptic dynamics can be explained by a parallel atomistic resistor network model. In addition, it is shown that such a device scheme can generally be realized in other 2D vdW semiconductors, such as MoS2 , MoSe2 , MoTe2 , and WSe2 . Demonstration of these atomically thin photo-memtransistor arrays, where the synaptic weights can be tuned for the atomistic defect density, provides implications for a new type of artificial neural networks for parallel matrix computations with an ultrahigh integration density.

Transcriptome of Epibiont Saccharibacteria Nanosynbacter lyticus Strain TM7x During the Establishment of Symbiosis.

Saccharibacteria Nanosynbacter lyticus strain TM7x is a member of the broadly distributed candidate phylum radiation. These bacteria have ultrasmall cell sizes, have reduced genomes, and live as epibionts on the surfaces of other bacteria. The mechanisms by which they establish and maintain this relationship are not yet fully understood. The transcriptomes of the epibiont TM7x and its host bacteria Schaalia odontolytica strain XH001 were captured across the establishment of symbiosis during both the initial interaction and stable symbiosis. The results showed a dynamic interaction with large shifts in gene expression for both species between the initial encounter and stable symbiosis, notably in transporter genes. During stable symbiosis, the host XH001 showed higher gene expression for peptidoglycan biosynthesis, mannosylation, cell cycle and stress-related genes, whereas it showed lower expression of chromosomal partitioning genes. This was consistent with the elongated cell shape seen in XH001 infected with TM7x and our discovery that infection resulted in thickened cell walls. Within TM7x, increased pili, type IV effector genes, and arginine catabolism/biosynthesis gene expression during stable symbiosis implied a key role for these functions in the interaction. Consistent with its survival and persistence in the human microbiome as an obligate epibiont with reduced de novo biosynthetic capacities, TM7x also showed higher levels of energy production and peptidoglycan biosynthesis, but lower expression of stress-related genes, during stable symbiosis. These results imply that TM7x and its host bacteria keep a delicate balance in order to sustain an episymbiotic lifestyle. IMPORTANCE Nanosynbacter lyticus type strain TM7x is the first cultivated member of the Saccharibacteria and the candidate phyla radiation (CPR). It was discovered to be ultrasmall in cell size with a highly reduced genome that establishes an obligate epibiotic relationship with its host bacterium. The CPR is a large, monophyletic radiation of bacteria with reduced genomes that includes Saccharibacteria. The vast majority of the CPR have yet to be cultivated, and our insights into these unique organisms to date have been derived from only a few Saccharibacteria species. Being obligate parasites, it is unknown how these ultrasmall Saccharibacteria, which are missing many de novo biosynthetic pathways, are maintained at a high prevalence within the human microbiome as well as in the environment.

Copper-Nanocoated Ultra-Small Cells in Grain Boundaries Inside an Extinct Vent Chimney.

Chemosynthetic organisms flourish around deep-sea hydrothermal vents where energy-rich fluids are emitted from metal sulfide chimneys. However, microbial life hosted in mineral assemblages in extinct chimneys lacking fluid venting remains largely unknown. The interior of extinct chimneys remains anoxic where the percolation of oxygenated seawater is limited within tightly packed metal sulfide grains. Given the scarcity of photosynthetic organics in deep seawater, anaerobic microbes might inhabit the grain boundaries energetically depending on substrates derived from rock-water interactions. In this study, we reported ultra-small cells directly visualized in grain boundaries of CuFeS2 inside an extinct metal sulfide chimney from the southern Mariana Trough. Nanoscale solid analyses reveal that ultra-small cells are coated with Cu2O nanocrystals in grain boundaries enriched with C, N, and P. In situ spectroscopic and spectrometric characterizations demonstrate the distribution of organics with amide groups and a large molecular organic compound in the grain boundaries. We inferred that the ultra-small cells are anaerobes because of the fast dissolution of Cu2O nanocrystals in oxygenated solution. This Cu2O property also excludes the possibility of microbial contamination from ambient seawater during sampling. It is shown by 16S rRNA gene sequence analysis that the chimney interior is dominated by Pacearchaeota known to have anaerobic metabolisms and ultra-small cells. Our results support the potential existence of photosynthesis-independent microbial ecosystems in grain boundaries in submarine metal sulfides deposits on the early Earth.

Robust Ru-N metal-support interaction to promote self-powered H2 production assisted by hydrazine oxidation

Electrocatalytic overall water splitting is hailed as the most promising approach to sustainably produce hydrogen on big scale, but the sluggish anodic oxygen evolution reaction (OER) with large operating potential results in the enormous energy consumption. To couple the cathodic hydrogen evolution reaction (HER) with low-potential hydrazine oxidation reaction (HzOR) is highly promising to significantly reduce the input cell voltage of water electrolysis, which requires high-performance bifunctional HER and HzOR electrocatalysts. Herein, a new-type Ru nanoparticle/mesoporous N-doped carbon (Ru/MPNC) composite is readily constructed with greatly exposed ultrafine Ru particles fused into N-doped carbon walls, and stabilized by in situ formed robust Ru-N metal-support interaction inherently stemming from the particular precursor, thus exhibiting superior bifunctional HER and HzOR activity, far surpassing commercial Pt/C. Furthermore, the two-electrode electrolyzer only require an ultrasmall cell voltage of 0.149 V to achieve 50 mA cm-2, which can be also easily driven by a direct hydrazine-H2O2 fuel cell to attain a decent H2 production rate of 0.893 mmol h−1. The theoretical calculations uncover the robust integration of Ru with NC can tailor the electronic property of exposed Ru sites, endowing the decreased water dissociation energy barrier, together with optimized adsorption free energies of H* and dehydrogenation intermediates of N2H4.

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Analysis of microbial communities in Binh Chau hot spring through metagenomic DNA sequencing

Binh Chau hot spring locates in Bung Rieng commune, Xuyen Moc district, Ba Ria - Vung Tau province, and is the second hottest hot spring in Vietnam. Up to date, the microbial diversity of this hot spring has been mainly evaluated using the culture-dependent methods, thus, it could not be able to assess all of microorganisms there. In this report, the microbial community of Binh Chau hot spring was investigated by meta-analysis using Hiseq Illumina for sequencing. The results revealed that only 106,903 genes were annotated and 49,190 genes were unknown among 156,093 potential ORFs. The annotated genes consisted of 29,069 bacterial genes, 1,416 archaeal genes, 4 eukaryotic genes, 3 viral genes, and 76,411 unclassified genes. Among the annotated and classified genes, the microbial community of Binh Chau hot spring was characterized by the predominance of bacteria over archaea. At the phylum level, the most abundant phyla in Binh Chau hot spring were followed as Proteobacteria > Firmicutes > Cyanobacteria > Bacteroidetes > Planctomycetes > Thaumarchaeota > Actinobacteria > Euryarchaeota. These belonged mainly to the thermophilic group. A number of the phyla are reported to grow at high temperature, alkaline pH, and high salt concentrations. In addition to the culturable species, the metagenomic data is also indicated the presence of unculturable groups, for example phylum Acidobacteria and Chloroflexi of bacteria. The order Thermoplasmata, which is classified to class Thermoplasmatales of the phylum Euryarchaeota, as well as ultra-small cell and symbiotic archaea including phyla Parvarchaeota, Nanohaloarchaeota, and Nanoarchaeota were detected. The results in this study indicated an important insight into the microbial communities of Binh Chau hot spring, which revealed a promising thermophilic gene sources for their exploitation and conservation in Vietnam.

Dual Nanoislands on Ni/C Hybrid Nanosheet Activate Superior Hydrazine Oxidation‐Assisted High‐Efficiency H2 Production

AbstractClean hydrogen evolution through electrochemical water splitting underpins various innovative approaches to the pursuit of sustainable energy conversion technologies, but it is blocked by the sluggish anodic oxygen evolution reaction (OER). The hydrazine oxidation reaction (HzOR) has been considered as one of the most promising substitute for OER to improve the efficiency of hydrogen evolution reaction (HER). Herein, we construct novel dual nanoislands on Ni/C hybrid nanosheet array: one kind of island represents the part of bare Ni particle surface, while the other stands for the part of core–shell Ni@C structure (denoted as Ni‐C HNSA), in which exposed Ni atoms and Ni‐decorated carbon shell perform as active sites for HzOR and HER respectively. As a result, when the current density reaches 10 mA cm−2, the working potentials are merely −37 mV for HER and ‐20 mV for HzOR. A two‐electrode electrolyzer exhibits superb activity that only requires an ultrasmall cell voltage of 0.14 V to achieve 50 mA cm−2.

Dual Nanoislands on Ni/C Hybrid Nanosheet Activate Superior Hydrazine Oxidation-Assisted High-Efficiency H2 Production.

Clean hydrogen evolution through electrochemical water splitting underpins various innovative approaches to the pursuit of sustainable energy conversion technologies, but it is blocked by the sluggish anodic oxygen evolution reaction (OER). The hydrazine oxidation reaction (HzOR) has been considered as one of the most promising substitute for OER to improve the efficiency of hydrogen evolution reaction (HER). Herein, we construct novel dual nanoislands on Ni/C hybrid nanosheet array: one kind of island represents the part of bare Ni particle surface, while the other stands for the part of core-shell Ni@C structure (denoted as Ni-C HNSA), in which exposed Ni atoms and Ni-decorated carbon shell perform as active sites for HzOR and HER respectively. As a result, when the current density reaches 10 mA cm-2 , the working potentials are merely -37 mV for HER and -20 mV for HzOR. A two-electrode electrolyzer exhibits superb activity that only requires an ultrasmall cell voltage of 0.14 V to achieve 50 mA cm-2 .

Down-Scalable and Ultra-fast Memristors with Ultra-high Density Three-Dimensional Arrays of Perovskite Quantum Wires.

With strikingly high speed, data retention ability and storage density, resistive RAMs have emerged as a forerunning nonvolatile memory. Here we developed a Re-RAM with ultra-high density array of monocrystalline perovskite quantum wires (QWs) as the switching matrix with a metallic silver conducting pathway. The devices demonstrated high ON/OFF ratio of ∼107 and ultra-fast switching speed of ∼100 ps which is among the fastest in literature. The devices also possess long retention time of over 2 years and record high endurance of ∼6 × 106 cycles for all perovskite Re-RAMs reported. As a concept proof, we have also successfully demonstrated a flexible Re-RAM crossbar array device with a metal-semiconductor-insulator-metal design for sneaky path mitigation, which can store information with long retention. Aggressive downscaling to ∼14 nm lateral dimension produced an ultra-small cell effectively having 76.5 nm2 area for single bit storage. Furthermore, the devices also exhibited unique optical programmability among the low resistance states.

Coupling Co2P/CoSe2 heterostructure nanoarrays for boosting overall water splitting.

Exploiting environmentally friendly and robust electrocatalysts for overall water splitting is of utmost importance in order to alleviate the excessive global energy consumption and climate change. Herein, a simple phosphoselenization method was used to prepare Co2P and CoSe2 coupled nanosheet and nanoneedle composite materials on nickel foam (Co2P/CoSe2/NF). Density functional theory calculations showed that Co2P had a higher water adsorption energy compared with CoSe2, indicating that H2O molecules are strongly adsorbed on the active sites of Co2P, which speeds up the kinetic process of water splitting. The Co2P/CoSe2-300 material displayed superior electrocatalytic activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline medium. It's worth noting that the Co2P/CoSe2-300 composite material nanoarrays merely needed an ultralow overpotential of 280 mV to drive a current intensity of 100 mA cm-2 for OER. In addition, when a two-electrode system was constructed for overall water splitting, the current intensity of 20 mA cm-2 could be reached while requiring an ultrasmall cell voltage of 1.52 V, which is one of the best catalytic activities reported up to now. Experimental and density functional theory calculations showed that the superior electrocatalytic performance of Co2P/CoSe2-300 could be attributed to its higher electron-transfer rate, higher water adsorption energy, and the synergistic effect of Co2P and CoSe2. Our work provides a novel approach for the one-step construction of composite materials as environmentally friendly and inexpensive water splitting catalysts.

Electronic Modulation of Hierarchical Spongy Nanosheets toward Efficient and Stable Water Electrolysis.

The energy conversion efficiency of water electrolysis is determined by the activity of selected catalysts. Ideal catalysts should possess not only porous architecture for high-density assembly of active sites but also a subtle electronic configuration for the optimized activity at each site. In this context, the development of stable porous hosting materials that allow the incorporation of various metal elements is highly desirable for both experimental optimization and theoretical comparison/prediction. Herein, MOF-derived spongy nanosheet arrays constructed by assembly of carbon encapsulated hetero-metal doped Ni2 P nanoparticles is presented as a superior bifunctional electrocatalyst for water splitting. This hierarchical structure can be stably retained when secondary metal dopants are introduced, providing a flexible platform for electronic modulation. The catalytic origin of activity enhancement via metal (Fe, Cr, and Mn) doping is deciphered through experimental and theoretical investigations. Combining the advantages in both morphological and electronic structures, the optimized catalyst NiMn-P exhibits remarkable activity in both hydrogen and oxygen evolution in the alkaline media, with an ultrasmall cell voltage of 1.49V (at 10mA cm-2 ) and high durability for at least 240 h.