Qingxuan Ren

Abstract For hydrogen generation from alkaline sodium borohydride (NaBH 4 ) solution, Co–Fe–B catalysts with different Co/(Co + Fe) molar ratios (χ Co ) were prepared by the chemical reduction of CoCl 2 and FeCl 3 ethanol solution with KBH 4 solution. The X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the as‐prepared Co–Fe–B catalysts were in amorphous form and ultrafine. The hydrogen generation measurements showed that as‐prepared Co–B and Co–Fe–B catalysts exhibited excellent catalytic activity. Co–Fe–B with the Co/(Co + Fe) molar ratio (χ Co ) of 0.85 was the best. Its maximum hydrogen generation rate at 298 K was 4,310 mL min –1 g –1 , while the Co–B was 2,773 mL min –1 g –1 . The enhanced activity could be attributed to large active surface area, electron transfer from B and Fe to active Co sites, and improvement in the dispersion of Co–B with Fe 2 O 3 . The activation energy of Co–Fe–B catalyst with the molar ratio χ Co = 0.85 was decreased to 29.09 kJ mol –1 as compared to 30.85 kJ mol –1 obtained with Co–B.

<h2>Summary</h2> Zero-gap membrane electrode assembly (MEA) electrolyzers are commonly used in electrochemical CO₂ reduction due to their high energy efficiency. While previous research has predominantly focused on catalyst development and membrane electrode and device design, temperature—a critical factor with the potential for significant impact on electrochemical CO₂ reduction—has been relatively overlooked. To address this gap in knowledge, we conducted a study using copper and silver as representative electrocatalysts to comprehensively examine the influence of temperature on zero-gap MEA CO₂ electrolyzers. Our investigation involved assessing selectivity, activity, and stability across a range of temperature conditions (30°C–70°C). We observed that the device efficiency consistently improves with rising temperature and that optimal reaction temperatures vary for different catalysts and products. Furthermore, temperature impacts the water balance of the system, with a moderate temperature increase proving beneficial for stability. These findings enhance the understanding of temperature effects in electrochemical CO₂ reduction and offer valuable insights for advancing CO₂ reduction technologies.