Boosting CO2 Electroreduction on N,P-Co-doped Carbon Aerogels

Electroreduction of CO₂ to CO powered by renewable electricity is a possible alternative to synthesizing CO from fossil fuel. However, it is very hard to achieve high current density at high faradaic efficiency (FE). Here, the first use of N,P-co-doped carbon aerogels (NPCA) to boost CO₂ reduction to CO is presented. The FE of CO could reach 99.1 % with a partial current density of −143.6 mA cm⁻², which is one of the highest current densities to date. NPCA has higher electrochemical active area and overall electronic conductivity than that of N- or P-doped carbon aerogels, which favors electron transfer from CO₂ to its radical anion or other key intermediates. By control experiments and theoretical calculations, it is found that the pyridinic N was very active for CO₂ reduction to CO, and co-doping of P with N hinder the hydrogen evolution reaction (HER) significantly, and thus the both current density and FE are very high.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Highly Efficient Porous Carbon Electrocatalyst with Controllable N‐Species Content for Selective CO2 Reduction

We report a straightforward strategy to design efficient N doped porous carbon (NPC) electrocatalyst that has a high concentration of easily accessible active sites for the CO₂ reduction reaction (CO₂RR). The NPC with large amounts of active N (pyridinic and graphitic N) and highly porous structure is prepared by using an oxygen‐rich metal–organic framework (Zn‐MOF‐74) precursor. The amount of active N species can be tuned by optimizing the calcination temperature and time. Owing to the large pore sizes, the active sites are well exposed to electrolyte for CO₂RR. The NPC exhibits superior CO₂RR activity with a small onset potential of ?0.35 V and a high faradaic efficiency (FE) of 98.4 % towards CO at ?0.55 V vs. RHE, one of the highest values among NPC‐based CO₂RR electrocatalysts. This work advances an effective and facile way towards highly active and cost‐effective alternatives to noble‐metal CO₂RR electrocatalysts for practical applications.     

Atomically Dispersed Nickel(I) on an Alloy‐Encapsulated Nitrogen‐Doped Carbon Nanotube Array for High‐Performance Electrochemical CO2 Reduction Reaction

Single‐atom catalysts (SACs) show great promise for electrochemical CO₂ reduction reaction (CRR), but the low density of active sites and the poor electrical conduction and mass transport of the single‐atom electrode greatly limit their performance. Herein, we prepared a nickel single‐atom electrode consisting of isolated, high‐density and low‐valent nickel(I) sites anchored on a self‐standing N‐doped carbon nanotube array with nickel–copper alloy encapsulation on a carbon‐fiber paper. The combination of single‐atom nickel(I) sites and self‐standing array structure gives rise to an excellent electrocatalytic CO₂ reduction performance. The introduction of copper tunes the d‐band electron configuration and enhances the adsorption of hydrogen, which impedes the hydrogen evolution reaction. The single‐nickel‐atom electrode exhibits a specific current density of ?32.87 mA cm^?2 and turnover frequency of 1962 h^?1 at a mild overpotential of 620 mV for CO formation with 97 % Faradic efficiency.     

CO2 Overall Splitting by a Bifunctional Metal‐Free Electrocatalyst

Photo/electrochemical CO₂ splitting is impeded by the low cost‐effective catalysts for key reactions: CO₂ reduction (CDRR) and water oxidation. A porous silicon and nitrogen co‐doped carbon (SiNC) nanomaterial by a facile pyrolyzation was developed as a metal‐free bifunctional electrocatalyst. CO₂‐to‐CO and oxygen evolution (OER) partial current density under neutral conditions were enhanced by two orders of magnitude in the Tafel regime on SiNC relative to single‐doped comparisons beyond their specific area gap. The photovoltaic‐driven CO₂ splitting device with SiNC electrodes imitating photosynthesis yielded an overall solar‐to‐chemical efficiency of advanced 12.5 % (by multiplying energy efficiency of CO₂ splitting cell and photovoltaic device) at only 650 mV overpotential. Mechanism studies suggested the elastic electron structure of ?Si(O)?C?N? unit in SiNC as the highly active site for CDRR and OER simultaneously by lowering the free energy of CDRR and OER intermediates adsorption.     

MoP Nanoparticles Supported on Indium‐Doped Porous Carbon: Outstanding Catalysts for Highly Efficient CO2 Electroreduction

Electrochemical reduction of CO₂ into value‐added product is an interesting area. MoP nanoparticles supported on porous carbon were synthesized using metal–organic frameworks as the carbon precursor, and initial work on CO₂ electroreduction using the MoP‐based catalyst were carried out. It was discovered that MoP nanoparticles supported on In‐doped porous carbon had outstanding performance for CO₂ reduction to formic acid. The Faradaic efficiency and current density could reach 96.5 % and 43.8 mA cm^?2, respectively, when using ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate as the supporting electrolyte. The current density is higher than those reported up to date with very high Faradaic efficiency. The MoP nanoparticles and the doped In₂O₃ cooperated very well in catalyzing the CO₂ electroreduction.     

Metal‐Free Fluorine‐Doped Carbon Electrocatalyst for CO2 Reduction Outcompeting Hydrogen Evolution

The electrochemical CO₂ reduction (ECDRR), as a key reaction in artificial photosynthesis to implement renewable energy conversion/storage, has been inhibited by the low efficiency and high costs of the electrocatalysts. Herein, we synthesize a fluorine‐doped carbon (FC) catalyst by pyrolyzing commercial BP 2000 with a fluorine source, enabling a highly selective CO₂‐to‐CO conversion with a maximum Faradaic efficiency of 90 % at a low overpotential of 510 mV and a small Tafel slope of 81 mV dec^?1, outcompeting current metal‐free catalysts. Moreover, the higher partial current density of CO and lower partial current density of H₂ on FC relative to pristine carbon suggest an enhanced inherent activity towards ECDRR as well as a suppressed hydrogen evolution by fluorine doping. Fluorine doping activates the neighbor carbon atoms and facilitates the stabilization of the key intermediate COOH* on the fluorine‐doped carbon material, which are also blocked for competing hydrogen evolution, resulting in superior CO₂‐to‐CO conversion.     

Increasing the CO2/N2 Selectivity with a Higher Surface Density of Pyridinic Lewis Basic Sites in Porous Carbon Derived from a Pyridyl‐Ligand‐Based Metal–Organic Framework

The development of functional porous carbon with high CO₂/N₂ selectivity is of great importance for CO₂ capture. In this paper, a type of porous carbon with doped pyridinic sites (termed MOFC) was prepared from the carbonization of a pyridyl‐ligand based MOF. Four MOFCs derived from different carbonizing temperatures were prepared. Structural studies revealed high contents of pyridinic‐N groups and nearly the same pore‐size distributions for these MOFCs. Gas‐sorption studies revealed outstanding CO₂ uptake at low pressures and room temperature. Owing to the high content of pyridinic‐N groups, the CO₂/N₂ selectivity on these MOFCs exhibits values of about 40–50, which are among the top values in carbon materials. Further correlation studies demonstrated that the CO₂/N₂ selectivities show a positive linear relationship with the surface density of pyridinic‐N groups, thus validating the synergistic effect of the doped pyridinic‐N groups on CO₂ adsorption selectivity.     

Thiol‐Assisted Synthesis of Carbon‐Supported Metal Nanoparticles for Efficient Electrocatalytic CO2 Reduction

The typical preparation route of carbon‐supported metallic catalyst is complex and uneconomical. Herein, we reported a thiol‐assisted one‐pot method by using 3‐mercaptopropionic acid (MPA) to synthesize carbon‐supported metal nanoparticles catalysts for efficient electrocatalytic reduction of carbon dioxide (CO₂RR). We found that the synthesized Au?MPA/C catalyst achieves a maximum CO faradaic efficiency (FE) of 96.2% with its partial current density of ?11.4 mA/cm², which is much higher than that over Au foil or MPA‐free carbon‐supported Au (Au/C). The performance improvement in CO₂RR over the catalyst is probably derived from the good dispersion of Au nanoparticles and the surface modification of the catalyst caused by the specific interaction between Au nanoparticles and MPA. This thiol‐assisted method can be also extended to synthesize Ag?MPA/C with enhanced CO₂RR performance.     

Highly Efficient Electroreduction of CO2 to C2+ Alcohols on Heterogeneous Dual Active Sites

Electroreduction of CO₂ to liquid fuels such as ethanol and n‐propanol, powered by renewable electricity, offers a promising strategy for controlling the global carbon balance and addressing the need for the storage of intermittent renewable energy. In this work, we discovered that the composite composed of nitrogen‐doped graphene quantum dots (NGQ) on CuO‐derived Cu nanorods (NGQ/Cu‐nr) was an outstanding electrocatalyst for the reduction of CO₂ to ethanol and n‐propanol. The Faradaic efficiency (FE) of C2+ alcohols could reach 52.4 % with a total current density of 282.1 mA cm^?2. This is the highest FE for C2+ alcohols with a commercial current density to date. Control experiments and DFT studies show that the NGQ/Cu‐nr could provide dual catalytic active sites and could stabilize the CH₂CHO intermediate to enhance the FE of alcohols significantly through further carbon protonation. The NGQ and Cu‐nr had excellent synergistic effects for accelerating the reduction of CO₂ to alcohols.     

A Graphene‐Supported Single‐Atom FeN5 Catalytic Site for Efficient Electrochemical CO2 Reduction

Electrochemical conversion of CO₂ into valued products is one of the most important issues but remains a great challenge in chemistry. Herein, we report a novel synthetic approach involving prolonged thermal pyrolysis of hemin and melamine molecules on graphene for the fabrication of a robust and efficient single‐iron‐atom electrocatalyst for electrochemical CO₂ reduction. The single‐atom catalyst exhibits high Faradaic efficiency (ca. 97.0 %) for CO production at a low overpotential of 0.35 V, outperforming all Fe‐N‐C‐based catalysts. The remarkable performance for CO₂‐to‐CO conversion can be attributed to the presence of highly efficient singly dispersed FeN₅ active sites supported on N‐doped graphene with an additional axial ligand coordinated to FeN₄. DFT calculations revealed that the axial pyrrolic nitrogen ligand of the FeN₅ site further depletes the electron density of Fe 3d orbitals and thus reduces the Fe–CO π back‐donation, thus enabling the rapid desorption of CO and high selectivity for CO production.     

Synthesis of High‐Surface‐Area Nitrogen‐Doped Porous Carbon Microflowers and Their Efficient Carbon Dioxide Capture Performance

Sustainable carbon materials have received particular attention in CO₂ capture and storage owing to their abundant pore structures and controllable pore parameters. Here, we report high‐surface‐area hierarchically porous N‐doped carbon microflowers, which were assembled from porous nanosheets by a three‐step route: soft‐template‐assisted self‐assembly, thermal decomposition, and KOH activation. The hydrazine hydrate used in our experiment serves as not only a nitrogen source, but also a structure‐directing agent. The activation process was carried out under low (KOH/carbon=2), mild (KOH/carbon=4) and severe (KOH/carbon=6) activation conditions. The mild activated N‐doped carbon microflowers (A‐NCF‐4) have a hierarchically porous structure, high specific surface area (2309 m² g^?1), desirable micropore size below 1 nm, and importantly large micropore volume (0.95 cm³ g^?1). The remarkably high CO₂ adsorption capacities of 6.52 and 19.32 mmol g^?1 were achieved with this sample at 0 °C (273 K) and two pressures, 1 bar and 20 bar, respectively. Furthermore, this sample also exhibits excellent stability during cyclic operations and good separation selectivity for CO₂ over N₂.     

Nitrogen‐Doped Carbon Nanotube Arrays for High‐Efficiency Electrochemical Reduction of CO2: On the Understanding of Defects,Defect Density,and Selectivity

Nitrogen‐doped carbon nanotubes (NCNTs) have been considered as a promising electrocatalyst for carbon‐dioxide‐reduction reactions, but two fundamental chemistry questions remain obscure: 1) What are the active centers with respect to various defect species and 2) what is the role of defect density on the selectivity of NCNTs? The aim of this work is to address these questions. The catalytic activity of NCNTs depends on the structural nature of nitrogen in CNTs and defect density. Comparing with pristine CNTs, the presence of graphitic and pyridinic nitrogen significantly decreases the overpotential (ca. ?0.18 V) and increases the selectivity (ca. 80 %) towards the formation of CO. The experimental results are in congruent with DFT calculations, which show that pyridinic defects retain a lone pair of electrons that are capable of binding CO₂. However, for graphitic‐like nitrogen, electrons are located in the π* antibonding orbital, making them less accessible for CO₂ binding.     

A Comparative Study of CO Oxidation on Nitrogen‐ and Phosphorus‐Doped Graphene

The geometry, electronic structure, and catalytic properties of nitrogen‐ and phosphorus‐doped graphene (N‐/P‐graphene) are investigated by density functional theory calculations. The reaction between adsorbed O₂ and CO molecules on N‐ and P‐graphene is comparably studied via Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) mechanisms. The results indicate that a two‐step process can occur, namely, CO+O₂→CO₂+O_ads and CO+O_ads→CO₂. The calculated energy barriers of the first step are 15.8 and 12.4 kcal mol^?1 for N‐ and P‐graphene, respectively. The second step of the oxidation reaction on N‐graphene proceeds with an energy barrier of about 4 kcal mol^?1. It is noteworthy that this reaction step was not observed on P‐graphene because of the strong binding of O_ads species on the P atoms. Thus, it can be concluded that low‐cost N‐graphene can be used as a promising green catalyst for low‐temperature CO oxidation.     

Molecular Evidence for Metallic Cobalt Boosting CO2 Electroreduction on Pyridinic Nitrogen

Nitrogen‐doped carbon materials (N‐C_mat) are emerging as low‐cost metal‐free electrocatalysts for the electrochemical CO₂ reduction reaction (CO₂RR), although the activities are still unsatisfactory and the genuine active site is still under debate. We demonstrate that the CO₂RR to CO preferentially takes place on pyridinic N rather than pyrrolic N using phthalocyanine (Pc) and porphyrin with well‐defined N‐C_mat configurations as molecular model catalysts. Systematic experiments and theoretic calculations further reveal that the CO₂RR performance on pyridinic N can be significantly boosted by electronic modulation from in‐situ‐generated metallic Co nanoparticles. By introducing Co nanoparticles, Co@Pc/C can achieve a Faradaic efficiency of 84 % and CO current density of 28 mA cm^?2 at ?0.9 V, which are 18 and 47 times higher than Pc/C without Co, respectively. These findings provide new insights into the CO₂RR on N‐C_mat, which may guide the exploration of cost‐effective electrocatalysts for efficient CO₂ reduction.     

Selective Electrochemical Reduction of Carbon Dioxide to Ethanol on a Boron‐ and Nitrogen‐Co‐doped Nanodiamond

Electrochemical reduction of CO₂ to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO₂ to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B‐ and N‐co‐doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO₂ to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (−1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co‐doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO₂ reduction revealed by DFT computation was CO₂→*COOH→*CO→*COCO→*COCH₂OH→*CH₂OCH₂OH→CH₃CH₂OH.     

Biomass‐derived Nitrogen and Phosphorus Co‐doped Hierarchical Micro/mesoporous Carbon Materials for High‐performance Non‐enzymatic H2O2 Sensing

Nitrogen and phosphorus co‐doped hierarchical micro/mesoporous carbon (N,P‐MMC) was prepared by simple thermal treatment of freeze‐dried okra in the absence of any other additives. The 0.96 wt % of N and 1.47 wt % of P were simultaneously introduced into the graphitic framework of N,P‐MMC, which also possesses hierarchical porous structure with mesopores centered at 3.6 nm and micropores centered at 0.79 nm. Most importantly, N,P‐MMC carbon exhibits excellent catalytic activity for electrocatalytic reduction of H₂O₂, resulting in a new strategy to construct non‐enzymatic H₂O₂ sensor. The N,P‐MMC‐based H₂O₂ sensor displays two linear detection range about 0.1 mM–10 mM (R²=0.9993) and 20 mM–200 mM (R²=0.9989), respectively. The detection limit is estimated to be 6.8 μM at a signal‐to‐noise ratio of 3. These findings provide insights into synthesizing functional heteroatoms doped porous carbon materials for biosensing applications.     

Highly Efficient CO2 Electroreduction on ZnN4‐based Single‐Atom Catalyst

The electrochemical reduction reaction of carbon dioxide (CO2RR) to carbon monoxide (CO) is the basis for the further synthesis of more complex carbon‐based fuels or attractive feedstock. Single‐atom catalysts have unique electronic and geometric structures with respect to their bulk counterparts, thus exhibiting unexpected catalytic activities. A nitrogen‐anchored Zn single‐atom catalyst is presented for CO formation from CO2RR with high catalytic activity (onset overpotential down to 24 mV), high selectivity (Faradaic efficiency for CO (FE_CO) up to 95 % at ?0.43 V), remarkable durability (>75 h without decay of FE_CO), and large turnover frequency (TOF, up to 9969 h^?1). Further experimental and DFT results indicate that the four‐nitrogen‐anchored Zn single atom (Zn‐N₄) is the main active site for CO2RR with low free energy barrier for the formation of *COOH as the rate‐limiting step.     

Polyoxometalate and Resin‐Derived P‐Doped Mo2C@N‐Doped Carbon as a Highly Efficient Hydrogen‐Evolution Reaction Catalyst at All pH Values

A new type of P‐doped Mo₂C coated by N‐doped carbon (P‐Mo₂C@NC) has been successfully prepared by calcining a mixture of H₃[PMo₁₂O₄₀] polyoxometalates (POMs) and urea‐formaldehyde resin under an N₂ atmosphere. Urea‐formaldehyde resin not only serves as the carbon source to ensure carbonization but also facilitates the uniform distribution of POM precursors, which efficiently avoid the aggregation of Mo₂C particles at high temperatures. TEM analysis revealed that the average diameter of the Mo₂C particles was about 10 nm, which is coated by a few‐layer N‐doped carbon sheet. The as‐prepared P‐Mo₂C@NC displayed excellent hydrogen‐evolution reaction (HER) performance and long‐term stability in all pH environments. To reach a current density of 10 mA cm^?2, only 109, 159, and 83 mV were needed for P‐Mo₂C@NC in 0.5 m H₂SO₄ (pH 0), 0.1 m phosphate buffer (pH 7), and 1 m KOH (pH 14), respectively. This could provide a high‐yield and low‐cost method to prepare uniform nanosized molybdenum carbides with highly efficient and stable HER performance.     

A Precious‐Metal‐Free Hybrid Electrolyzer for Alcohol Oxidation Coupled to CO2‐to‐Syngas Conversion

Electrolyzers combining CO₂ reduction (CO₂R) with organic substrate oxidation can produce fuel and chemical feedstocks with a relatively low energy requirement when compared to systems that source electrons from water oxidation. Here, we report an anodic hybrid assembly based on a (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) electrocatalyst modified with a silatrane‐anchor ( STEMPO ), which is covalently immobilized on a mesoporous indium tin oxide (mesoITO) scaffold for efficient alcohol oxidation (AlcOx). This molecular anode was subsequently combined with a cathode consisting of a polymeric cobalt phthalocyanine on carbon nanotubes to construct a hybrid, precious‐metal‐free coupled AlcOx–CO₂R electrolyzer. After three‐hour electrolysis, glycerol is selectively oxidized to glyceraldehyde with a turnover number (TON) of ≈1000 and Faradaic efficiency (FE) of 83 %. The cathode generated a stoichiometric amount of syngas with a CO:H₂ ratio of 1.25±0.25 and an overall cobalt‐based TON of 894 with a FE of 82 %. This prototype device inspires the design and implementation of nonconventional strategies for coupling CO₂R to less energy demanding, and value‐added, oxidative chemistry.