Borohydride Oxidation-Water Reduction Fuel Cells Advanced by Local Hydroxyl Enrichment-Inhibited Borohydride Hydrolysis on Cu(0) Sites

Energy Chemistry Chemistry Catalysis Energy Engineering Engineering Materials Science
fuel cell borohydride hydrolysis copper doping cobalt phosphide electrocatalysis

Academic Background

Direct Borohydride Fuel Cells (DBFCs), as a potential carbon-neutral energy source, have attracted considerable attention due to their use of sodium borohydride (NaBH4) as the anode fuel. NaBH4 possesses advantages such as portability, non-toxicity, water solubility, and environmental stability, allowing DBFCs in theory to deliver up to 1.64 V in voltage and 9.3 kWh/kg in energy density. However, traditional DBFCs face two major challenges in practical applications: the slow kinetics of cathodic oxygen reduction reaction (ORR), and the low selectivity of the anodic borohydride oxidation reaction (BOR), resulting in insufficient output power density and efficiency for industrial demands.

To address these issues, researchers have proposed a new type of borohydride fuel cell (BHFC), which replaces the conventional ORR with acidic hydrogen evolution reaction (HER) to achieve efficient power generation and concurrent hydrogen production. By employing interface engineering and local environment modulation strategies, a highly selective BOR catalyst was designed in this study, which significantly suppresses the hydrolysis of NaBH4 and thereby enhances the performance of the fuel cell.

Source of the Paper

This paper was co-authored by Libo Zhu, Chang Chen, Tiantian Wu, and others from the State Key Laboratory of High-Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences. The corresponding authors are Xiangzhi Cui and Jianlin Shi. The paper was published on March 13, 2025 in the journal Chem, entitled “Borohydride Oxidation-Water Reduction Fuel Cells Advanced by Local Hydroxyl Enrichment-Inhibited Borohydride Hydrolysis on Cu(0) Sites”.

Research Process

1. Catalyst Design and Synthesis

Researchers designed and synthesized a catalyst consisting of copper-doped cobalt phosphide (CoP) nanosheet arrays grown on copper foam (Cu–CoP/CF). The catalyst was prepared via a two-step method involving electrodeposition and phosphating: firstly, Co(OH)2 nanosheets were grown on copper foam, followed by phosphating treatment to obtain Cu–CoP/CF.

2. Catalyst Characterization

Detailed characterization of the catalyst was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The results showed that Cu–CoP/CF maintained the nanosheet array morphology and that Cu was successfully doped into the CoP phase, forming a Cu3P phase.

3. Electrocatalytic Performance Testing

The HER performance of the catalyst was tested under acidic conditions, and the results demonstrated that Cu–CoP/CF exhibited excellent HER activity and stability in 0.5 M H2SO4, with an overpotential of only 39 mV and no significant current density decay over 700 hours. Under alkaline conditions, Cu–CoP/CF also displayed outstanding BOR performance, with an overpotential of -49 mV and stability maintained for 260 hours.

4. Local Environment Modulation Mechanism

Using in situ X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR), researchers found that during the BOR process, surface Cu(I) in Cu–CoP/CF was reduced by NaBH4 to Cu(0), creating a local environment rich in OH-, thereby suppressing the hydrolysis of NaBH4 and significantly improving the selectivity of BOR.

5. Fuel Cell Performance Testing

The researchers assembled a BHFC, using Cu–CoP/CF as both anode and cathode catalyst, and tested its electrochemical performance. The results showed that the peak power density of the BHFC reached 114 mW/cm², while the hydrogen production rate at the cathode was at least 40 mol/h/m², significantly surpassing that of the conventional DBFC.

Main Results

  1. Catalyst Characterization: Cu–CoP/CF maintained the nanosheet array morphology, and Cu was successfully doped into the CoP phase, forming a Cu3P phase.
  2. HER Performance: Cu–CoP/CF demonstrated excellent HER activity and stability under acidic conditions, with an overpotential of only 39 mV and no significant current density decay over 700 hours.
  3. BOR Performance: Cu–CoP/CF showed outstanding BOR performance under alkaline conditions, with an overpotential of -49 mV and remained stable for 260 hours.
  4. Local Environment Modulation: During the BOR process on Cu–CoP/CF, surface Cu(I) was reduced by NaBH4 to Cu(0), creating a local OH–enriched environment, suppressing the hydrolysis of NaBH4 and significantly improving BOR selectivity.
  5. Fuel Cell Performance: The BHFC achieved a peak power density of 114 mW/cm² and a hydrogen production rate at the cathode of at least 40 mol/h/m².

Conclusion and Significance

Through interface engineering and local environment modulation strategies, this study designed a highly selective BOR catalyst that significantly suppresses the hydrolysis of NaBH4, thereby improving the performance of borohydride fuel cells. The BHFC not only efficiently generates electricity but also enables concurrent hydrogen production, demonstrating substantial scientific value and application prospects. This research provides a new strategy for the development of efficient borohydride fuel cells and promotes the advancement of carbon-neutral energy technologies.

Research Highlights

  1. Highly Selective BOR Catalyst: By Cu doping and local hydroxyl enrichment, the hydrolysis of NaBH4 is significantly suppressed and the selectivity of BOR is improved.
  2. Excellent HER and BOR Performance: Cu–CoP/CF exhibits outstanding electrocatalytic activity and stability under both acidic and alkaline conditions.
  3. Highly Efficient Fuel Cell Performance: The BHFC achieves a peak power density of 114 mW/cm² and a hydrogen production rate at the cathode of at least 40 mol/h/m².
  4. Local Environment Modulation Mechanism: Through in situ reduction of Cu(I) to Cu(0), a local OH–enriched environment is formed to suppress the hydrolysis of NaBH4.

Other Valuable Information

The study also utilized density functional theory (DFT) and in situ Fourier transform infrared spectroscopy (FTIR) to deeply investigate the reaction mechanism of BOR, further confirming the crucial role of Cu doping in enhancing BOR selectivity. These findings provide theoretical basis and experimental support for the development of efficient borohydride fuel cells.